// Workers AI · dad joke modeWhat did the electronic color code say? "I'm wired to match.

A 2.26 kΩ, 1%-precision resistor with 5 color bands (E96 series), from top, 2-2-6-1-1; the last two brown bands indicate the multiplier (×10) and the tolerance (1%).

An electronic color code is a system which wordlessly identifies either the functions of cables and connections, or the types and variants of electronic components. Codes for cables and connections range from the use of pink, blue, and green connectors on computer sound cards, to early attempts at standardizing the colors of battery, loudspeaker, and antenna wires of radio sets in the 1920s, to the 25-pair color code, used in telecommunications cables. Among the component identification applications, those used on resistors are most widespread, with usage on inductors also popular, while in the past, many variations were applied to capacitors, diodes, and other part types.

History

RMA resistor color code guide, ca. 1945–1950

Computer components marked with color bands; resistors with beige background, inductors with turquoise, and capacitors with greenish and yellowish backgrounds.

Before standardization, some manufacturers used their own color codings on the fixed resistors in their radio sets, seemingly choosing a random color for each part stock number. Then, in 1930, a new code started coming into wide usage among radio makers. This new style encoded the resistance value of each part by means of one background paint color and usually, two additional paint marks. The Radio Manufacturers Association (RMA) gave its endorsement of this coding around 1931. This all-over painted, "body-end-dot" coding style, while most vividly associated with pre-war radio equipment, did live on for a while, and was still in use in the 1960s.

In 1935, advertisements appeared for resistors coded with a sequence of color bands including one acting as a tolerance indicator; the RMA adopted a standard for this alternative style by 1941. A 1943 reference book, Mechanical Practice gives an early description of a further development. While the 1935 banded style only called for two digit bands before the band that specifies a "multiplying value", coded as an exponent, the new variation had three, bringing the total number of bands including the tolerance to five, as opposed to just three or four. This might seem to indicate that even at that early date, the use of a four–five rule became necessary in decoding banded resistors; in going from four to five in the total count of bands, that is where the number of digit-encoding bands increases from two to three, moving the exponent band from the third to the fourth position. In practice this was not a very important rule to memorize back then, as actual resistors showing the three-digit coding innovation remained scarce for twenty years afterwards. Eight decades later, application of the rule in some form is routinely required, but now a big part of the art of reading random-sourced resistors is, recognizing the exceptions, those tricky cases where resistance codings do not follow the rule.

Over many decades, as the organization name changed (RMA, RTMA, RETMA, EIA) so was the name of the code. Though known most recently as EIA color code, the four name variations are found in books, magazines, catalogs, and other documents over more than 95 years.

In 1952, the International Electrotechnical Commission (IEC) published a fork of the RMA's banded resistor concept as IEC 62:1952; although it did not expand to include three-digit codings following a four–five rule until the 1974 edition, its successors and national versions/translations are widely referenced today. Starting with the 1968 edition it added in the widely used "RKM codes" for printed text component values on resistors and capacitors. Successive revisions, up to the current IEC 60062:2016, added more optional features to the resistor color code, but also diverged from the EIA versions.

One standardized color code scheme for capacitors was in use by 1934, although some radio makers kept using random-picked color codes on these longer than they did on resistors. (At that point, most were still calling these "condensers", an older term.) There were many variations of flat postage stamp/domino-style mica and paper dielectric capacitors with paint dots; tubular capacitors with a sequence of spots or bands also date to the 1940s. Eventually many more styles were produced using mica, paper, ceramic, glass, and plastics for the dielectric, also many tantalum types, not all codings directly published by the RMA and successors, some with dots, some with bands, some with layer-dipped paint. A 1949 article detailed nine marking types in use by that time, but the proliferation of styles was just getting started then. Some later ceramic-dielectric ones from the VCR era of roughly 1980 onward look a lot like modern small axial-leaded resistors. Today, while color-coded "caps" are less commonly encountered, the layer-dipped "tropical fish" ones are still preferred by some, and recent reproductions of certain old tubular capacitor types have been embellished with replica "bumble-bee" color bands, suitable to make any classic-style electric guitar more authentic.

Schemes for color-coding small inductors, (A.K.A. radio frequency chokes, coils, etc.) were in use by 1950; as with the capacitors, some types do look a lot like modern small resistors. For reading, while many recent ones decode like common resistors, giving an inductance value in microhenries, older ones and some current ones are more complicated; unlike resistors, a gold or silver band may be at either end, or both, and there may be no exponent band.

Small semiconductor diodes/rectifiers were being marked with color bands by 1958. Some Zener/avalanche-breakdown diodes have paint bands that indicate their main characteristic of interest, which is, their nominal rated Zener voltage. More commonly, a type number is indicated using one of several variants that support the U.S. JEDEC "1N" series (Glass diodes marked this way were common in the 1960s.) and European Pro Electron numbering schemes. Proprietary arbitrary codings were used by some; Hitachi made diodes with bands of designer colors such as "verdure" and "yellow ocher". Many later-production glass diodes have only one or two color bands, indicating a broad type category.

Several complex color coding systems for plastic-cased transistors were in use in the Soviet sphere. The U.S. standard for diodes allows application to transistors but seems to have been little used for this. Usually when color markings are found on U.S.-style small plastic transistors that have printed numbering also, they indicate a bin-sort code or something proprietary.

By 1970, disc-shaped thermistors and voltage dependent resistors/varistors were being made with color coding in the form of layer-dipped paint; these may be confused with some ceramic disk capacitors which are painted similarly. There are also tubular, axial-leaded styles of varistors which have their own look which differentiates them from other components.

There is even a color band coding standard for fuses, published in 1988 as IEC 127, and adopted in national variants covering both cartridge types that look like fuses and also, miniature types that look like modern small resistors.

The paint pigment used for the number seven, according to some British sources, is supposed to be a "dark violet"; others in the British Commonwealth have called it mauve. The general consensus of references world-wide through the decades would be a simple violet, although, in the early years there are several sources that call it purple, and even a vote for lavender may be found.

The color band system is easily readable by people with good color vision and from multiple directions, if well-chosen paints are used. Fairly early on, some manufacturers put printed numbers on as an additional identifying aid. Some might say the system is poorly designed, as it would be simple enough to choose ten colors that work for most color blind people.

Color bands were used because they were easily and cheaply printed on tiny components. However, there were drawbacks, especially for color blind people. Overheating of a component or dirt accumulation may make it impossible to distinguish brown from red or orange. Advances in printing technology have now made printed numbers more practical on small components. The values of components in many surface mount packages are marked with printed alphanumeric codes instead of a color code.

Resistors

One decade of the E12 series (there are twelve preferred values per decade of values) shown with their electronic color codes on resistors

A 0 Ω resistor (zero ohm), marked with a single black band

The resistance value is given by two or three color markings (usually rings/bands starting at the head end, or rarer, partial bands or spots, or, in the oldest style, the body/background and optional end mark) indicating numeric digits plus one more giving a "multiplying value" which is specified by an exponent. The multiplying value is ten raised to the power of the exponent; for the ten positive valued colors that is just a one followed by zeroes. After the exponent, a tolerance indicator band and sometimes one more may follow, making up to six bands in total. The system is similar to scientific notation, but it differs in its normalization rules. In the normalized scientific notation representation of any number, the first nonzero digit is the "units," or "ones" place. A denormalized case, where some other position is the first nonzero digit, may often be encountered in the intermediate steps required when adding or multiplying two numbers, before the final step of re-normalizing. But in resistor coding, the first nonzero digit is the tens or hundreds place, depending on whether there are two or three digit bands, with exceptions of some low-end resistance values. These exceptions, where the sequence starts with black/zero, are the denormalized resistor codings, used when the lowest available color for the exponent is not low enough otherwise. For example, the number fifty-six thousand is $5.6\times 10^{4}$ in normalized scientific notation. A 2% tolerance resistor of that many ohms, not nearly low enough to need a black first band, may be coded with two or three digit bands; it may read:

$56\times 10^{3}$ with markings green(5)-blue(6)-orange(3)-red(2%) or,

$560\times 10^{2}$ with markings green(5)-blue(6)-black(0)-red(2)-red(2%).

This gives the two equivalent parts different colors for their exponent bands. Doing a rough sort of mixed resistors might involve using a row of jars, with one jar for each exponent color (third band) of the two-digit coded resistors, and also a second row with a jar for each exponent color (fourth band) of the three-digit coded ones. A 56000 ohm resistor might be then found in the 2 digit oranges or the 3 digit reds. The main difficulties in this process are getting the correct reading orientation on some of the smaller resistors, and, identifying each resistor as a two- or three-digit coding, to determine which row it goes in. If all the resistors were made conforming to the EIA and IEC standards, they would all follow the four–five rule, where four and fewer bands always imply there are two digit bands before the exponent, while five or more always mean there are three digit bands. In practice, many resistors will be found where the rule has been flouted or disregarded.

Many call the numeric digits given by the up-front color bands "significant digits", "significant figures", or, in the current IEC standard, "significant numerals". Pedants might argue that the word "significant" is misleading unless much arcane explanatory text is added, (this being almost never provided,) so it might be better to use a term like "numeric digits," "marked digits," or "coded digits" instead.

Some coding diagrams may be considered misleading, implying that a two-digit resistor is like a three-digit one that has lost its ones/units-digit, rather than correctly showing the hundreds digit being lost.

Some sources give graphic decoding keys that make it look like, in going from a four- to a five-band resistor, the new band is added as the middle position, and going from a five- to a four-band resistor, it is the middle one that is lost. These may foster the false presumption that a five-band resistor whose middle band is black, which decodes to zero, should have the same value as the four-band code obtained by rubbing out the black band.

The current IEC standards have no requirement to have any coordination between the tolerance band color and the choice to use 2 or 3 digit-coding bands. There have been attempts to enforce such a correspondence; the 1943 source Mechanical Practice opined that the 1% and even 2% tolerance indication should be permitted only for the 3-digit marking case, but this was never followed to any extent at the time. Eventually the IEC standards prescribed only the 2 digit practice for every supported tolerance including 1% until 1974. Typical current practice uses 3 digits for 1% or better, 2 digits for 5% and up; 2% tolerance may be found either way. Exceptions with 3 digit coding and a gold, 5% tolerance band can be found; sometimes this has been done in order to support a sixth solid band to indicate a temperature stability specification by IEC practice. A gold or even silver tail-end band on a 3-digit, 5-band coding could result simply from following EIA RS-279 and RS-196-A, prescribing 3-digit coding on "film-type" resistors, or to mark a 1 gigohm resistor without needing to go beyond violet for the exponent band.

Color code markings are less likely to be used on resistors of very low or very high values, large power resistors, and very tight-tolerance parts, as these would be considered "specialty" rather than "commodity" products, with a need to print extra information. On Surface-mount technology PC boards, however, sometimes the more specialized resistors are the color-coded ones; a digital multimeter may contain a few color-banded precision types in the leadless "MELF" case surrounded by many typographically-marked "chip" type resistors.

Color sequence system

Orientation for reading

Resistors requiring varying degrees of finesse in identifying the correct reading orientation. Also available as a zoomable svg file

Reading color-sequence resistors requires first identifying the head and tail ends; decoding charts typically show a resistor with the head end at the left, so the code reads left to right. Difficulty of this task varies; the easiest case applies if, anywhere other than as the middle band of the sequence, there is at least one gold or silver band. This metallic-paint "Shiny" points out the tail end; it does not have to be the extreme end band, or even second from the end, and might not be the "tolerance band." The same applies to a pink, or salmon-pink band, if it is not just a faded violet. (If there is a Shiny at each end, or on both sides of the middle of the sequence, that is probably an inductor, misclassified as a resistor.)

If that fails, step two is to look for one of the more obscure, but still reliable and definitive, orientation indications. For old-style plastic-encased molded flat resistors with spots rather than bands, the type easily confused with vintage flat capacitors, there may be a molded-in arrow pointing from head to tail, and supposedly there are (rare, photo not available, but defined by IEC) resistors with five plain bands plus a dotted or interrupted sixth band; this indicates the tail. More commonly, there can be a single paint dot or broken band separating four solid bands from a fifth; this is also a tail end indication. If one of the inter-band gaps is widened to fit text characters or a logo, that also is a tail-end indication even if it separates three bands, at the head, from two more, at the tail.

If none of these apply, three less-foolproof clues based on band widths and spacing may have to be used, with finesse applied in case of a conflict.

The first clue is the margin test. Looking at the open margin space beyond the two ends of the color sequence, the closer, tighter end is suggested as the head. Ideally, this should be reliable in all cases regardless of the number of bands. (Or spots or broken bands, in some cases.) Pedants might argue that the IEC standard requires manufacturers to make this a sufficient and conclusive indicator, with no other clues needed, and if people would follow the rules, "That would be great." But some might object that this would take away much of the sport involved. Anybody could read all the resistors then! This test is pretty reliable for cases of three, and often four, bands not resolved above, but for small five- and six-band resistors, there are many sloppy ones out there where it is best to consider this a weak indication, potentially outweighed by one or both of the others, especially if the margin difference is small.

For the second clue, the gap test, if one of the inter-band gap widths exceeds all the others by a noticeable amount, and it is the gap next to one of the end bands, that can be a fair evidence of the tail end even if the gap doesn't have printing or a paint dot in it. Greater gap size implies a stronger evidence.

And thirdly, for the width test, on a five- or six-band resistor where one band is the widest by about 50% or more over all the others, this can be a tail end indicator if it seems to be following modern IEC conventions. This includes any six-band resistor where the wide band is an end band or second from the end, where this is strong evidence of that being the tail end. And, even on a five-band resistor with a small, modern-looking glossy, painted or epoxy body, having the wide band as one of the end bands, that is still a fair evidence of that being the tail end. A brown plastic background or terminal ends of the tube showing a different color or material are examples of resistors that are not "modern looking" and may instead have their head-end band widened. On some resistors following a long-established U.S. practice, a double-wide head-end band indicates a wirewound resistor.

Considering these three tests, if at least one of them gives a direction indication, and there is no conflict among them, that is a cause for celebration. Otherwise, the strengths of the three indications may have to be weighed, and there is still no guarantee that plain sloppy marking will not leave an ambiguity. A hybrid of the three clues may also be of value, where the two end bands are ignored, and the margin test done on the remaining (1 to 4) bands. Other arcane tests may help with some five-band resistors, especially those where the middle band is the only Shiny. If only one orientation gives a value and appropriate tolerance color according to the standard value lists, there may be a temptation to assume deviations from those lists cannot exist, but in practice, exceptions may be found which only give a standard value when read wrong/backwards.

Haphazardly marked 1 percent tolerance resistors with five rather evenly-spaced bands, centered on the part, are widely available in assortment packs. With these, there are worthwhile shortcuts that work on certain value ranges, like, if one end band of a resistor is not brown, that is the head, (This works for all values not starting with digit "1") and, for the under-10 megohm values common in low voltage work, if one of the second-from-the-end bands is a color value 5 or greater (green through white) that also indicates the head end. Some 1% standard-value codings are symmetrical and read the same either way; but also, two different standard-value resistors may be mirrorings of each other.

Decoding the value

Once the head end is identified, a code table or mnemonic gives a numeric equivalent for each of the bands that encode the value. For resistors known to be in strict accordance with IEC or EIA standards, decoding the value in ohms involves using the four–five rule to determine whether to take two or three digits from the bands at the head end, and then adjusting the resulting integer according to the exponent band which follows, at position three or four. For an exponent band of gold, silver, or pink, that means dividing by 10, 100, or 1000, respectively; these are the colors whose numeric value is negative. For the other exponent colors, it is just a matter of adding the indicated number of trailing zeroes, or, none for black.

A band following the exponent band specifies the tolerance rating; if only three-bands, 20% is generally assumed. A three-digit resistor may encode a temperature stability or temperature coefficient of resistance (TCR) rating, in units of ppm/K, with a sixth solid band, or a color dot or interrupted band on either side of the fifth solid band, or by a helical/diagonal mark crossing the five solid bands.

Here is an example of a two-digit, four-band resistor:

1. The first significant figure of component value (left side)
2. The second significant figure (some precision resistors have a third significant figure, and thus five bands).
3. The decimal multiplier (number of trailing zeroes, or power of 10 multiplier)
4. If present, indicates tolerance of value in percent (no band means 20%)

In the above example, a resistor with bands of red, violet, green, and gold has first digit 2 (red; see table below), second digit 7 (violet), followed by 5 (green) zeroes: 2700000 ohms. Gold signifies that the tolerance is ±5%.

All coded components have at least two value bands and a multiplier; other bands are optional.

The standard color code per IEC 60062:2016 is as follows:

Ring Colour			Significant numeral	Multiplier		Tolerance		TCR, Temperature coefficient
Name	Code	RAL				Percent [%]	Letter	[ppm/K]	Letter
None	–	–	–	–		±20	M	–
Pink	PK	3015	–	×10−3	×0.001	–		–
Silver	SR	–	–	×10−2	×0.01	±10	K	–
Gold	GD	–	–	×10−1	×0.1	±5	J	–
Black	BK	9005	0	×100	×1	–		±250	U
Brown	BN	8003	1	×101	×10	±1	F	±100	S
Red	RD	3000	2	×102	×100	±2	G	±50	R
Orange	OG	2003	3	×103	×1000	±0.05	W	±15	P
Yellow	YE	1021	4	×104	×10000	±0.02	P	±25	Q
Green	GN	6018	5	×105	×100000	±0.5	D	±20	Z
Blue	BU	5015	6	×106	×1000000	±0.25	C	±10	Z
Violet	VT	4005	7	×107	×10000000	±0.1	B	±5	M
Grey	GY	7000	8	×108	×100000000	±0.01	L (A)	±1	K
White	WH	1013	9	×109	×1000000000	–		–

Ring Colour			Significant numeral	Multiplier		Tolerance		TCR, Temperature coefficient
Name	Code	RAL				Percent [%]	Letter	[ppm/K]	Letter
None	–	–	–	–		±20	M	–
Pink	PK	3015	–	×10−3	×0.001	–		–
Silver	SR	–	–	×10−2	×0.01	±10	K	–
Gold	GD	–	–	×10−1	×0.1	±5	J	–
Black	BK	9005	0	×100	×1	–		±250	U
Brown	BN	8003	1	×101	×10	±1	F	±100	S
Red	RD	3000	2	×102	×100	±2	G	±50	R
Orange	OG	2003	3	×103	×1000	±0.05	W	±15	P
Yellow	YE	1021	4	×104	×10000	±0.02	P	±25	Q
Green	GN	6018	5	×105	×100000	±0.5	D	±20	Z
Blue	BU	5015	6	×106	×1000000	±0.25	C	±10	Z
Violet	VT	4005	7	×107	×10000000	±0.1	B	±5	M
Grey	GY	7000	8	×108	×100000000	±0.01	L (A)	±1	K
White	WH	1013	9	×109	×1000000000	–		–

Ring Colour			Significant numeral	Multiplier		Tolerance		TCR, Temperature coefficient
Name	Code	RAL				Percent [%]	Letter	[ppm/K]	Letter
None	–	–	–	–		±20	M	–
Pink	PK	3015	–	×10−3	×0.001	–		–
Silver	SR	–	–	×10−2	×0.01	±10	K	–
Gold	GD	–	–	×10−1	×0.1	±5	J	–
Black	BK	9005	0	×100	×1	–		±250	U
Brown	BN	8003	1	×101	×10	±1	F	±100	S
Red	RD	3000	2	×102	×100	±2	G	±50	R
Orange	OG	2003	3	×103	×1000	±0.05	W	±15	P
Yellow	YE	1021	4	×104	×10000	±0.02	P	±25	Q
Green	GN	6018	5	×105	×100000	±0.5	D	±20	Z
Blue	BU	5015	6	×106	×1000000	±0.25	C	±10	Z
Violet	VT	4005	7	×107	×10000000	±0.1	B	±5	M
Grey	GY	7000	8	×108	×100000000	±0.01	L (A)	±1	K
White	WH	1013	9	×109	×1000000000	–		–

Standardized resistors follow various E series of preferred numbers for their specific values, which are determined by their tolerance. These values repeat for every decade of magnitude: ... 0.68, 6.8, 68, 680, ... For resistors of 20% tolerance the E6 series, with six values: 10, 15, 22, 33, 47, 68, then 100, 150, ... is used; each value is approximately the previous value multiplied by ⁶√10. For 10% tolerance resistors the E12 series, with ¹²√10 as multiplier, is used; similar schemes up to E192, for 0.5% or tighter tolerance are used. The separation between the values is related to the tolerance so that adjacent values at the extremes of tolerance approximately just overlap; for example, in the E6 series 10 + 20% is 12, while 15 − 20% is also 12. A surprising variety of additional random values may also be available from stock at major suppliers.

Exceptions to IEC practice; code sequence variations

There are many exceptions to the IEC/EIA prescribed sequence diagrams to watch for, some rare, some pretty common. All of these generally started out with someone deciding to take the four–five rule more like a suggestion. A five-band resistor, following the rule, and current IEC standards, is like a four-band one with an extra digit band, the hundreds place, added at the head end. But in many cases instead a band is added at the tail, to indicate a widely variable piece of gratuitous random information, making a five-band resistor with only two coded digit bands. It may be hard to figure out what this added band is saying, but a bigger problem is that on a random-sourced five-band resistor, presence or absence of a gratuitous fifth band re-defines all the other bands. A 1986 article details how, for example, a pair of identically-marked resistors with the fifth band of red could have two different values, if one is a 2% tolerance, three-digit part made according to IEC/EIA rules, and one is a two-digit resistor with red gratuitous fifth band. Many decoding keys do not see this issue as rating a mention.

Through the years, gratuitous fifth bands have been used to specify information such as a reliability rating, (yellow, orange, possibly other very rare ones, on brown plastic background, under old U.S. military spec.; made in the 1960s through 1997) or a lead solderability rating, (white or rare green,, also per US military specs.) or a temperature stability characteristic, or a "Grade 1 high-stability" attribute, (salmon pink according to U.K. standard "RIC/112", 1950s and 1960s; may fade to white) or an indication that the tolerance is by "total excursion". (colored as a repeat of the regular tolerance band, from the U.K. in the 1960s.)

The gratuitous fifth band may also specify the amperage and temperature rating of an internal thermal fuse on an "over temperature protector" resistor, or indicate some other attribute such as fusible in general, fusible wirewound, flameproof, flameproof fusible "failsafe" wirewound, high-voltage, anti-surge, fusible anti-surge, high-power (compact) wirewound, non-inductive wirewound, a "discharge path resistor," even high sound quality types for audiophiles. A mix of black, white, brown, red, yellow, green, blue, and violet are all found on current active products. The specific example cited in that 1986 article involved a temperature stability indicator band, which is now much less common as a gratuitous fifth, but, for example, a false-twin resistor pair with violet fifth bands can be readily obtained today. And possibly, a false twin of a common three-digit, 1% or 2% tolerance resistor might be found among recent two-digit parts with brown or red gratuitous fifth band, supplied by several manufacturers.

Resistors presenting various difficulty levels in separating the adherents and exceptions to the four–five rule implicit in IEC/EIA standards. Also available as a zoomable svg file

A strategy for classifying five-band resistors, into the standards-conformant three-digit and rule-breaking two-digit categories, may involve multiple clues. To start out, the two-digit with gratuitous-fifth case can be assumed for any with a (possibly faded) salmon-pink tail-end band or either Shiny or plain pink as the middle band. And, resistors with the old-style brown plastic casing and a silver or gold fourth band, go with the twos if the fifth band is orange or yellow; also blue, green, gray or violet if the first band is double-width. Any specimen where the last two bands are a matching pair of brown, red, orange, green, violet, gold, or silver is a possible total-excursion resistor. If these two are slightly thinner, and are separated from the first three by an (at least slightly) oversized gap, or especially if there is a "w" logo in the gap, that may be considered a confirmation of this type. These go with the twos.

Among resistors that can be excluded from being the total-excursion type, (any that do not have one of those color pairs, or that can be presumed not to be from the U.K. in the 1960s,) any that have a fourth band other than silver, gold, brown, or red can generally be assumed to be threes. And with them go any resistors having a random printed typographic code or a temperature stability indicator color dot between the fourth and fifth bands, or with temperature stability indicated with a helical/slash mark. For the leadless surface-mount cylindrical resistors, there are some two-digit ones with a gold fourth and yellow gratuitous fifth in a 3 by 9 millimeter size, unusually large for this type of package, but the rest of the known leadless five-band types are threes.

But now, due to running out of clues with quite a few possibly unresolved, it may be time start going by what is likely to be encountered, rather than what theoretically could exist. For one thing, putting any remaining ones having a black, yellow, or orange fifth band in with the twos should be safe except for rather rare, tighter-than-0.1%-tolerance resistors. The same might be said for white, of which many two-digit examples can be found, with the caveat that three-digit resistors with a white fifth for 0.02% tolerance are in a current Yageo product line and just might be found in precision equipment.

Specimens with a black third and gold fourth band decode to the same value either way, leaving only the tolerance in question. If only one of the two decoding schemes gives a standard value with an appropriate tolerance color according to the standard value lists, although not an infallible indication, this may be taken as a strong clue. For any remainders it might be helpful to have pictures showing the general look of some current-production gratuitous-fifth types such as Vitrohm's CRT series with brown, red, and orange, JEPSUN's and Firstohm's PPR and SSR series with red, Vishay's and Yageo's with violet, and a few vintage ones with a temperature stability indicator or a green solderability indication as the gratuitous fifth.

Possible candidates for finding a gratuitous-fifth resistor with coding to match a very common three-digit, 1% tolerance resistor, with a brown fifth band, could include one from the Vitrohm CRT series; offered values include 120 ohms 5%, whose false twin would be a standard E96 value, 12.1 Ohms.

After discarding the fifth band, the gratuitous-fifth types decode their value and tolerance as a common two-digit four-band resistor, (However, see below in case of a white or gray exponent band...) but there is also an even more exotic five-band exception. Supposedly the Yageo-Vitrohm RXS series resistors, if under 0.1 ohms value, will be like an IEC-conformant four-band resistor except that one silver and one gold band replace the pink exponent band. With silver as the middle band color, these would not be confused with the normal three-digit type, but they may masquerade as a relatively normal gratuitous-fifth resistor of ten times their true resistance such as some of the Vishay-Draloric LCA series. (With their gold gratuitous fifth band, those too may have three Shinies in a row at their tail end.)

There are also cases where on a resistor with only four bands, the final one is a gratuitous addition to the IEC standard coding. Salmon-pink and yellow gratuitous fourth bands have sometimes been added to three-band resistors, positioned where a tolerance band is expected; other color examples may exist. These do not break the four–five rule, so they will not result in a false value reading.

Then is it safe to assume value coding exceptions will not be a problem on four-band resistors' values? Not really; there is another way to break the rule. Sometimes a four-band resistor may be like a three-digit five-band resistor with a suppressed/imaginary fifth band. The user is expected to know this is a special case, and that the missing/imagined tolerance band indicates maybe 1% rather than the traditional 20%. So a 56.2 ohm resistor could have the same coding (green-blue-red-gold, $562\times 10^{-1}$) as a common two-digit, 5600 ohm 5% resistor. In current production this may be limited to the small leadless-type resistors used for surface mounting but in past years, it has been done on certain very small (about 4 millimeters in length) leaded ones too.

And what about cases of other than four or five bands? Supposedly Yageo may place a yellow, violet or white gratuitous sixth band where IEC practice would only allow a temperature stability code band; with no violation of the four–five rule, the resistance would still be read correctly. For three or fewer bands there are more special cases. On a three-band resistor with a gap after the first two, this may be the equivalent of a canonical 10 to 99 milliohm four-band resistor with the wide gap in place of the pink exponent band called for under the current IEC standard. This goes beyond just breaking the four–five rule, as it changes the meaning of the third band from the exponent to the tolerance. Also, on uninsulated black carbon composition resistors, old references say any black paint bands may be omitted, so the full sequence may need to be mentally reconstructed.

Zero ohm resistors, marked with one or sometimes two black bands, are lengths of wire wrapped in a resistor-like body which can be mounted on a printed-circuit board (PCB) by automatic component-insertion equipment. A coding of four black bands has been used for an arbitrary large, (such as anything over 100 kilohm) resistor meant for use as a core for winding an inductance.

More exceptions to IEC practice; color definition inconsistencies

Historically not every manufacturer has followed the current IEC coding chart for tolerance band colors and, for grey and white, even the exponent band colors, which are important to the decoded resistance result. A listing of these variations follows:

Table of exponent and tolerance color variations for resistors (large, hidden by default)

Color Name	Numeric value (Negative values apply to exponents only.)	Exceptions to numeric value sometimes found as exponent on resistors	Resistance tolerance percentage, according to various sources
			1938 "Extended" code quoted in 1943's Mechanical Practice	Docs of U.S. military	Chart from Findlay 1959, widely reprinted in the '60s and '70s	EIA RS-279 (1963) and RS-196 (1970) for three-digit film resistors	Current IEC 60062 (2016)	Yageo Corp. precison resistor datasheet 2024	Coding published by Futaba Corp.	One Russian Language Source	High-voltage two-digit four-band resistor, per Vishay	Obscure British practice, c. 1950s	Likely meaning on two-digit resistor, inc. vintage parts	Likely meaning on three-digit resistor
None	–	−3	–	±20	±20	–	±20		±20	–	–	–	±20	±1
Pink	−3	–	–	–	–	–	–		–	–	–	–	–	–
Silver	−2	–	±10	±10	±10	±10	±10		±10	±10	–	±10	±10	±10
Gold	−1	–	±5	±5	±5	±5	±5		±5	±5	–	±5	±5	±5
Black	0	–	±20	±20	±20	–	–		±0.01	±0.005	–		±20	¯\_(ツ)_/¯
Brown	1	–	±1	±1	±1	±1	±1		±1	±1	–	–	±1	±1
Red	2	–	±2	±2	±2	±2	±2		±2	±2	–	±2	±2	±2
Orange	3	–	±3	±3	±3	–	±0.05		±0.02	±0.01	–	–	±3	±0.05
Yellow	4	–	±4	–	GMV	–	±0.02		±0.005	±0.02	±5	–	±5	±0.02
Green	5	–	±5	±5	±5	±0.5	±0.5		±0.5	±0.5	–	–	±5	±0.5
Blue	6	–	±6	±10	±6	±0.25	±0.25	±0.25	±0.25	±0.25	–	–	¯\_(ツ)_/¯	±0.25
Violet	7	–	±7	–	±12.5	±0.1	±0.1	±0.1	±0.1	±0.1	–	–	±7	±0.1
Gray/Grey	8	−3	±8	–	±30	±0.05	±0.01	±0.05	±0.05	±0.05	±10	–	¯\_(ツ)_/¯	±0.05 or ±0.01
White	9	−4;−3	±9	±2.5	±10	–	–	±0.02	–	–	–	±1	¯\_(ツ)_/¯	±0.02

Under current IEC or the early RMA standards, there should be nothing special about gray or white as the exponent band; gray means a resistance ten times the value of what it would be with violet, and white means ten times that. But documents of Yageo Corp. would make gray an alternate for IEC's pink, with white to be used on values too small for pink, for a numerical value of −4. And, Ohmite and at least one other manufacturer have used white for numerical exponent value −3, instead of IEC's pink. So, brown-black-gray could mean 1 gigohm or 0.01 ohm, and brown-black-white could be 10 gigohms or 0.01 ohm or 0.001 ohm.

To summarize the variations of the tolerance colors, only silver, gold, brown, and red have had their meanings unchanged since 1943, (on both two- and three-digit codings) and generally the rainbow colors beyond red will indicate a tolerance tighter than 1% on three-digit resistors, and looser than 2% on two-digit resistors.

As an aside, resorting to using an ohmmeter is always an option, but it gives different information than reading the color code does. It tells what the resistance is now; reading the code tells what it was supposed to be when it was new. To assess how well the part has aged, that takes both.

Body-end-dot system

The "body-end-dot" or "body-tip-spot" system was used for cylindrical composition resistors sometimes still found in very old equipment (built before the Second World War); the first band was given by the body color, the second band by the color of one end of the resistor, and the multiplier by a dot or band around the middle of the resistor. The other end of the resistor was in the body color, silver, or gold for 20%, 10%, 5% tolerance (tighter tolerances were not routinely used).

Examples

Example color-coded resistors

From top to bottom:

• Green, blue, black, black, brown
  • 560 ohms ±1%
• Red, red, orange, gold
  • 22000 ohms ±5%
• Yellow, violet, brown, gold
  • 470 ohms ±5%
• Blue, grey, black, gold
  • 68 ohms ±5%

The physical size of a resistor is indicative of the power it can dissipate.

There is an important difference between the use of three and of four bands to indicate resistance. The same resistance is encoded by:

• Red, red, orange = 22 followed by 3 zeroes = 22000 (excluding default, silver, or gold tolerance)
• Red, red, black, red = 220 followed by 2 zeroes = 22000 (excluding brown or other band for tolerance)

Mnemonics

Further information: List of electronic color code mnemonics

Pictorial color code mnemonic

Useful mnemonics have been created to make it easier to remember the color codes. Some of these provide a hash-like mapping—a 1:1 mental or pictural translation for each color. Others just give an ordered list. Suitability of these may vary; many do not put gold (−1) and silver (−2) and especially pink (−3) in their correct numerical order, if included at all:

• Betty Brown Runs Over Your Garden But Violet Gingerly Walks.
• Bad Bears Raid Our Yummy Grub But Veto Grey Waffles.
• BB ROY from Great Britain has a Very Good Wife.

The following example includes the tolerance codes — gold, silver and none:

• Bad Beer Rots Out Your Guts But Vodka Goes Well – Get Some Now.

The colors are sorted in ascending order of visible light photon frequency/energy like in a rainbow to make them easy to remember and to reduce the significance of possible read errors due to color shifts and fading over time: red (2), orange (3), yellow (4), green (5), blue (6), violet (7). Black (0) has no energy, brown (1) has a little more, white (9) has everything and grey (8) is like white, but less intense.

Capacitors

Capacitors may be marked with 4 or more colored bands or dots. The colors encode the first and second most significant digits of the value in picofarads, and the third color the decimal multiplier. Additional bands have meanings which may vary from one type to another. Low-tolerance capacitors may begin with the first 3 (rather than 2) digits of the value. It is usually, but not always, possible to work out what scheme is used by the particular colors used. Cylindrical capacitors marked with bands may look like resistors.

Color		Significant digits	Multiplier	Tolerance (%)	Characteristic	DC working voltage (V)	Operating temperature (°C)	EIA/vibration (Hz)
	Black	0	1	—	—	—	−55 to +70	10 to 55
	Brown	1	10	±1	B	100	—	—
	Red	2	100	±2	C	—	−55 to +85	—
	Orange	3	1000	—	D	300	—	—
	Yellow	4	10000	—	E	—	−55 to +125	10 to 2000
	Green	5	100000	±0.5	F	500	—	—
	Blue	6	1000000	—	—	—	−55 to +150	—
	Violet	7	10000000	—	—	—	—	—
	Grey	8	—	—	—	—	—	—
	White	9	—	—	—	—	—	EIA
	Gold	—	—	±5	—	1000	—	—
	Silver	—	—	±10	—	—	—	—

Extra bands on ceramic capacitors identify the voltage rating class and temperature coefficient characteristics. A broad black band was applied to some tubular paper capacitors to indicate the end that had the outer electrode; this allowed this end to be connected to chassis ground to provide some shielding against hum and noise pickup.

Polyester film and "gum drop" tantalum electrolytic capacitors may also be color-coded to give the value, working voltage and tolerance.

Postage stamp capacitors and war standard coding

Postage-stamp mica capacitors marked with the EIA 3-dot and 6-dot color codes, giving capacitance value, tolerance, working voltage, and temperature characteristic. This style of capacitor was used in vacuum-tube equipment.

Capacitors of the rectangular "postage stamp" form made for military use during World War II used American War Standard (AWS) or Joint Army-Navy (JAN) coding in six dots stamped on the capacitor. An arrow on the top row of dots pointed to the right, indicating the reading order. From left to right the top dots were: either black, indicating JAN mica, or silver, indicating AWS paper; first significant digit; and second significant digit. The bottom three dots indicated temperature characteristic, tolerance, and decimal multiplier. The characteristic was black for ±1000 ppm/°C, brown for ±500, red for ±200, orange for ±100, yellow for −20 to +100 ppm/°C, and green for 0 to +70 ppm/°C.

A similar six-dot code by EIA had the top row as first, second and third significant digits and the bottom row as voltage rating (in hundreds of volts; no color indicated 500 volts), tolerance, and multiplier. A three-dot EIA code was used for 500 volt 20% tolerance capacitors, and the dots signified first and second significant digits and the multiplier. Such capacitors were common in vacuum tube equipment and in surplus for a generation after the war but are unavailable now.

Inductors

Standards IEC 60062 / EN 60062 do not define a color code for inductors, but manufacturers of small inductors use the resistor color code, typically encoding inductance in microhenries. A white tolerance ring is used by TDK to indicate custom specifications.

Diodes

The part number for small JEDEC "1N"-coded diodes – in the form "1N4148" – is sometimes encoded as three or four rings in the standard color code, omitting the "1N" prefix. The 1N4148 would then be coded as yellow (4), brown (1), yellow (4), grey (8).

Wire

Transformer

Power transformers used in North American vacuum-tube equipment were often color-coded to identify the leads. Black was the primary connection, red secondary for the B+ (plate voltage), red with a yellow tracer was the center tap for the B+ full-wave rectifier winding, green or brown was the heater voltage for all tubes, yellow was the filament voltage for the rectifier tube (often a different voltage than other tube heaters). Two wires of each color were provided for each circuit, and phasing was not identified by the color code.

Audio transformers for vacuum tube equipment were coded blue for the finishing lead of the primary, red for the B+ lead of the primary, brown for a primary center tap, green for the finishing lead of the secondary, black for grid lead of the secondary, and yellow for a tapped secondary. Each lead had a different color since relative polarity or phase was more important for these transformers. Intermediate-frequency tuned transformers were coded blue and red for the primary and green and black for the secondary.

Other

Wires may be color-coded to identify their function, voltage class, polarity, phase or to identify the circuit in which they are used. The insulation of the wire may be solidly colored, or where more combinations are needed, one or two tracer stripes may be added. Some wiring color codes are set by national regulations, but often a color code is specific to a manufacturer or industry.

Building wiring under the US National Electrical Code and the Canadian Electrical Code is identified by colors to show energized, neutral, and grounding conductors, and to identify phases. Other color codes are used in the UK and other areas to identify building wiring or flexible cable wiring.

Mains electrical wiring, both in a building and on equipment, was once usually red for live, black for neutral, and green for earth, but this was changed as it was a hazard for color-blind people, who might confuse red and green; different countries use different conventions. Red and black are frequently used for positive and negative of battery or other single-voltage DC wiring.

Thermocouple wires and extension cables are identified by color code for the type of thermocouple; interchanging thermocouples with unsuitable extension wires destroys the accuracy of the measurement.

Automotive wiring is color-coded but standards vary by manufacturer; differing SAE and DIN standards exist.

Modern personal computer peripheral cables and connectors are color-coded to simplify connection of speakers, microphones, mice, keyboards and other peripherals, usually according to coloring schemes following recommendations such as PC System Design Guide, PoweredUSB, ATX, etc.

A common convention for wiring systems in industrial buildings is: black jacket – AC less than 1,000 volts, blue jacket – DC or communications, orange jacket – medium voltage 2,300 or 4,160 V, red jacket 13,800 V or higher. Red-jacketed cable is also used for relatively low-voltage fire alarm wiring, but has a much different appearance.

Local area network cables may also have non-standardised jacket colors identifying, for example, process control network vs. office automation networks, or to identify redundant network connections, but these codes vary by organization and facility.

See also

• E series of preferred numbers (IEC 60063) – series of preferred resistance and capacitance values
• Color code
• Electrical wiring – AC power wiring inside buildings, including standard color codes

External links

Online resistor calculators

• Multi-purpose resistor code converter (4 and 5 band, mobile-friendly, shows nearest standard value)
• 6 band resistor color code calculator (easy lookup, 4 and 5 band calculators also available)

Historical charts

• Wheel charts
• Reference charts