Talk:Tesla (unit)

Strongest magnetic field in a superconductor

Commercial superconducting NMR magnets reach 20T. Furthermore, the link in ref. [2] is broken. So this passage should be deleted or corrected. 132.230.182.55 (talk) 13:06, 7 May 2015 (UTC)

Miscellaneous

Please re-Explain the Explanation to provide a deeper conceptual image of this pseudo-scientific and impractical sounding phenomenon, and cite some sources!

---

"in the magnetic field of a huge horseshoe magnet 0,001 T,"

Hello, is this a typo? Can someone more experienced than I answer?

Sincerely,

Chris

This value 0f 0.001T is pretty low for a "huge" horseshoe magnet. Old fashioned magnets could create field of > 100 gauss, or 0.01T. More modern permanent rare-earth magnets have fields more like 10,000 gauss or about 1 Tesla.

Neil Bergstrom

Definition

The definition should be kg/C•s rather than kg/A•s². Amps are a derivative measurement from Coulombs and seconds which are the fundamental measurements involved. Given that it is given in several different forms, leaving kg/A•s² makes sense, but the SI base units should be corrected to use Coulombs rather than Amperes.

"SI base units should be corrected to use Coulombs rather than Amperes" - OK, so talk to CGPM and try persuading them. Meantime, your edits are undone.Evgeny (talk) 08:12, 8 June 2023 (UTC)

The definition should say unit of magnitic flux density, not magnetic field. — Preceding unsigned comment added by 2601:600:8D00:1100:4CDD:756C:BF2D:2778 (talk) 18:22, 26 April 2016 (UTC)

The definition shouldn't use the shorthand symbols only; it should have the definition in terms of the names of the units as well, to avoid confusion. --Starwed 20:15, 10 February 2006 (UTC)

And shouldn't the dashes in the various units (like m^-2) be the same length? They vary... ~Gertlex 18:02, 23 July 2006 (UTC)

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hey.. someone put this in terms someone not taking physics would understand. like.. the amount of 1gram paperclips a magnet could pick up at 1 tesla.

Your example would be measured in webers, not teslas. For tesla examples, see the list of examples in this article. --Heron 21:12, 6 April 2006 (UTC)

Copyedited and removed the following cruft:

>== SI multiples ==

>

SI multiples of tesla (T)

Submultiples			Multiples
Value	SI symbol	Name	Value	SI symbol	Name
10−1 T	dT	decitesla	101 T	daT	decatesla
10−2 T	cT	centitesla	102 T	hT	hectotesla
10−3 T	mT	millitesla	103 T	kT	kilotesla
10−6 T	μT	microtesla	106 T	MT	megatesla
10−9 T	nT	nanotesla	109 T	GT	gigatesla
10−12 T	pT	picotesla	1012 T	TT	teratesla
10−15 T	fT	femtotesla	1015 T	PT	petatesla
10−18 T	aT	attotesla	1018 T	ET	exatesla
10−21 T	zT	zeptotesla	1021 T	ZT	zettatesla
10−24 T	yT	yoctotesla	1024 T	YT	yottatesla
10−27 T	rT	rontotesla	1027 T	RT	ronnatesla
10−30 T	qT	quectotesla	1030 T	QT	quettatesla

Defining all these combinations of the SI units adds nothing to article

>== Explanation ==

>The tesla is the value of the total magnetic flux (a magnet's "power") divided by area. Hence, reducing >the affected area will generally increase the magnetic flux density.

>This will continue to occur until the material becomes magnetically saturated and/or the magnetic field >"leakage" increases so fast that no additional tesla gains are possible.

Makes no sense - what is being "reduced"? How does this have any relation to the definition of a unit?

84.92.241.186 22:55, 26 April 2007 (UTC)

Shouldn't n, the number of turns, be included when V or A are involved in the definition? Voltage should be volts/turn and current should be Ampere-Turns —Preceding unsigned comment added by 71.134.146.86 (talk) 00:23, 20 January 2010 (UTC)

a large 14 kg loudspeaker magnet will have a coil gap of 1 T

I find this hard to believe, as a tesla is quite a large flux density, so I have tagged it with {{Fact}}. S. Morrow 23:11, 28 October 2007 (UTC)

How many tesla is a maglev track? Or a magnetic induction rail for transportation?

I'm trying to find info on that detail. 68.83.179.156 (talk) 15:43, 13 November 2009 (UTC)

Yugoslavian?

The page says he's "Yugoslavian-American", but Tesla's own Wiki article says he was born in Austria, which is definitely not Yugoslavia. Yugoslavia is a part of Europe, which is stated on the Yugoslavia article. And before anyone complains to me about it, no, I won't edit it myself, because every edit I make is always reverted on Wikipedia, whether I'm trolling or not. —Preceding unsigned comment added by 74.195.230.26 (talk) 14:45, 22 March 2010 (UTC)

care to do some more homework before typing in here? Yugoslavia- does not exist anymore. And yes parts of former Yugoslavia were also part of Austrian-Hungarian Empire. Care to learn more about history? So all statements are correct: he is Serbian first and foremost.That is his nationality.But he could be considered Austrian and Yugoslavian as well.. Glad to be of help.

71.99.86.158 (talk) 17:26, 23 October 2010 (UTC)

"Electric vs Magnetic Field" what is this?

"Electric vs Magnetic Field

It's sometimes confusing as to the difference between magnetic field (in tesla) vs electric field strength. The difference is that a magnetic field is moving while an electric field isn't, this can be seen by looking at the units for each. Electric field is N/C, while magnetic field (in tesla) can be written as N/(C*m/s). Showing the difference between the 2 clearly is m/s, or movement. In ferromagnets the movement creating the magnetic field is the electron spin (and to a lesser extent electron orbital angular momentum). In current carrying wire (electromagnets) the movement the electrons move through the wire (whether the wire's straight or circular)."

Please remove this. It's badly written and barely makes any sense. Does anybody agree? --79.55.31.10 (talk) 14:12, 31 March 2011 (UTC)

Units are WRONG!

The SI base units for the tesla is wrong in the Wiki article. Consult WolframAlpha and other sources. — Preceding unsigned comment added by 66.108.188.165 (talk • contribs) 03:40, 21 September 2011 (UTC)

Huh? We can ignore this one. —Quondum 06:54, 19 February 2014 (UTC)

Conversions

The bulk of the Conversions section consists of unsourced claims about the unit's non-usage among engineers, (although several of the article's sources seem to indicate otherwise), and claims that publications that do use it (presumably including mainstream journals) 'often' capitalize the unit. The correction is then oddly worded:

"However, as with gauss and other units, even those derived from names (watt, joule) the unit is lower-case when written out..."

...seeing as the allegedly preferred gauss is also derived from a name. The paragraph should probably be removed per WP:NOR. AveVeritas (talk) 06:10, 19 February 2014 (UTC)

Agreed. Done. —Quondum 06:43, 19 February 2014 (UTC)

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Conflict of unit (T) with prefix (T)

Shouldn't there be a section describing the problem with this SI derived unit? All other official SI units (to my knowledge) are carefully designed to avoid conflict and ambiguity. But the tesla (unit) is given the symbol T, which is in direct conflict with the Terra (prefix) also a capital letter T.

For example, if one were to read 2.5 Tm, should that be interpreted as 2.5e+12 meters (a distance), or as 2.5 tesla*meters (a magnetic potential).

I read on the page about torque (as I recall) that the SI recommends, for example, Nm (newton-meter) to be used for torque, instead of mN (which is ambiguous -- it could mean meter-newton or milli-newton). But there is no discussion about the ambiguity with the symbol for tesla units -- which is a more serious problem in my opinion. I've been looking around for more info, and if I find it, I will update the article. Until then, any comments? Hydradix (talk) 01:38, 23 August 2016 (UTC)

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Conversion to gauss is incorrect

As of 2019, the coulomb and ampere are defined via a particular multiple of the charge on the electron. Accordingly, mu_0 is no longer exactly 4 \pi \times 10^{-7}. On the Vacuum permeability page the value is given as 4 \pi \times 0.99999999987(16) \times 10^{−7} H/m.

Statements to this effect should be included in this page. Mgolden (talk) 14:15, 30 May 2026 (UTC)

At present we merely say in Tesla#Conversion to non-SI units that One tesla is equivalent to: 10,000 (or 10⁴) G", and then recast that slightly, while the infobox simply has ≘ 10⁴ G. What value should we present, do we have a RS for that value, and would we need to explain that further in this article about the tesla, whether in body text or a footnote? NebY (talk) 15:12, 30 May 2026 (UTC)

Yes. This is discussed on the Vacuum permeability page. There's a reference to the CODATA page for \mu_0, where the value 4π × 10−7 N/A2 × [1 − (1.3 ± 1.6) × 10−10] is given. Apart from the particular value, it's important to make clear that the relationship is now an experimental result and Gauss and Tesla are no longer equivalent units. Mgolden (talk) 13:08, 2 June 2026 (UTC)

I can make the change unless someone disagrees. Mgolden (talk) 13:09, 2 June 2026 (UTC)

That's not what I'm asking. What number should we present in One tesla is equivalent to nnn G"? Do we have a reliable source which directly states that? NebY (talk) 13:28, 2 June 2026 (UTC)

Sorry my reply was unclear. The relationship between the gauss and the tesla is given by

${\frac {\mathrm {gauss} }{\mathrm {tesla} }}=10^{-5}{\sqrt {\frac {10^{9}\mu _{0}}{4\pi }}}$

The $10^{-5}$ comes from the ratio of the size of the dyne to the newton and the rest of it from the definitions of the statcoulomb and the coulomb. (Happy to produce the whole argument if necessary.)

Until 2019, the numerical value of $\mu _{0}$ was defined to be exactly $4\pi \times 10^{-7}$ so the value under the square root was exactly 100, and therefore 1 tesla was exactly $10^{4}$ gauss. Now instead we have

${\frac {\mathrm {gauss} }{\mathrm {tesla} }}=10^{-4}{\sqrt {1-(1.3\pm 1.6)\times 10^{-10}}}$

which is

${\frac {\mathrm {gauss} }{\mathrm {tesla} }}=10^{-4}(1-(6.5\pm 8)\times 10^{-11})$

or

${\frac {\mathrm {tesla} }{\mathrm {gauss} }}=10^{4}(1+(6.5\pm 8)\times 10^{-11})$

Obviously this is not a matter of great significance in practice, but I think it's important to understand the underlying significance of the 2019 change in the coulomb. Mgolden (talk) 18:35, 2 June 2026 (UTC)

So now One tesla is equivalent to approximately 10,000 (or 10⁴) G? Anything more would, I think, be off-topic in this article, being about the tesla, but our Gauss (unit) article (linked from this article, of course) might describe the change in that unit's definition. We would want to provide a source here that gives the relationship as directly as possible, considering WP:CALC. NebY (talk) 18:56, 2 June 2026 (UTC)

I agree that the gauss is off topic, but I wouldn't say that the change in the tesla is. There was a change in the definition of the ampere in 2019 and this implies a change in the definition of the tesla, since is is a derived unit depending on the ampere.

As shown on the CODATA page (https://physics.nist.gov/cgi-bin/cuu/Value?eqmu0), the new definition of $\mu _{0}$ is $4\pi \alpha \hbar /e^{2}c$, compared to an exact value of $4\pi \times 10^{-7}{\text{T}}\cdot {\text{m}}\cdot {\text{A}}^{-1}$ prior to 2019.

The values of $\hbar ,e$ and $c$ are now all exact,

https://physics.nist.gov/cgi-bin/cuu/Value?hbar

https://physics.nist.gov/cgi-bin/cuu/Value?e

https://physics.nist.gov/cgi-bin/cuu/Value?c

but $\alpha$ is measured

https://physics.nist.gov/cgi-bin/cuu/Value?alph

So $\mu _{0}$ is non-exact as well. This implies that a measurement of a field in tesla after 2019 is different from that measurement before 2019. In principle, everyone should adjust their recorded values for any magnetic field they measured in tesla before 2019 - but of course this would have no practical effect because the change was so small.

How about this?: we discuss this change on this page. In the section of non-SI units, mention only that the formulas are exact for the pre-2019 definition of the tesla, and say only that the post-2019 conversion will differ slightly but not give the conversion here. Mgolden (talk) 15:35, 3 June 2026 (UTC)

I should add, in case it wasn't clear. It isn't the gauss that changed. The gauss is part of a separate unit system and nothing was done to that. Mgolden (talk) 16:01, 3 June 2026 (UTC)

Ah, thanks for that clarification. Yes, as the effect was so small (less than one part in a billion), it's unlikely anyone's adjusting values. and likewise I guess for any other values affected by the 2019 or earlier redefinitions (ohms? or even metres, newtons, pascals etc, if we track back far enough into other SI redefinitions) - and I speak as someone who's still peeved about the absurd 1901 redefinition of the litre!

But I'd reverse your suggestion. We should give the current conversion here, as we do in other articles, and footnote any superseded value. We do still need a more direct source than NIST's page on vacuum magnetic permeability. NebY (talk) 13:08, 4 June 2026 (UTC)

First, I'd be okay with giving the current definition here.

No one will be adjusting their old measurements, as you said. The whole point of these changes is to define the unit is a more reliable way, without disturbing any old measurements. It does affect the conversion between the SI and Gaussian cgs units ones in this very small way, but it's rare for people to use Gcgs for real measurements! The only Gcgs unit commonly used in the real world is in fact the gauss, and that's because it has this nice round conversion factor and is a more reasonable size than the tesla.

What is pretty shocking is that searching for this I have not found a single site that mentions the 2019 redefinition of the ampere in this regard. There's been 7 1/2 years since the change was made, and almost none of the sites I have seen even discuss it, and none note that the change affects the relationship between gauss and tesla. Even, for example, the class notes from the Boston University class, which does mention the change at the end doesn't note that the 10,000 is no longer exact. https://physics.byu.edu/faculty/colton/docs/phy441-resources/gaussian-units.pdf

However, I think there's a way to use the CODATA value in a simpler way, without the complexity of what I wrote above.

In SI base units, the dimensions of $\mu _{0}$ are N/A$^{2}$. The current $\mu _{0}$ is $1-(1.3\pm 1.6)\times 10^{-10}$ times the pre-2019 $\mu _{0}$ (this is given on the Vacuum permeability page). The new ampere is therefore multiplied by a factor of the inverse of the square root of this compared to the pre-2019 ampere. The dimensions of the tesla are ${\frac {kg}{A\cdot s}}$, so the size of the tesla goes like the square root of size of $\mu _{0}$.

I think that's simple enough to pass muster. Mgolden (talk) 22:16, 4 June 2026 (UTC)

Oops - couple of things I just realized:

1) I should have said the units of $\mu _{0}$ are (kg-m)/(s$^{2}$-A^2)</math>. I think this means that I said some wrong things above, namely:

2) I was forgetting that the 2019 changes affected the kg as well, so that my calculation of the ratio of the old to new tesla needs to take that into account, which I didn't above.

3) The gauss was affected by the 2019 changes - because the gram is 1/1000 kg.

To fix this I'll need to find the value of the old kg in terms of the new kg. However, my calculation of the ratio of the new gauss to the new tesla is still correct! Mgolden (talk) 23:23, 4 June 2026 (UTC)

Thanks for all this, but I'm afraid your diligence has shown that we can't use it - which might also seem "pretty shocking"! Something that no-one else has noticed, or at least published in a reliable source for Wikipedia, epitomises original research as in our policy Wikipedia:No original research. That policy, in its application here and elsewhere, can mean that Wikipedia is behind or arguably inaccurate, and requires a particular self-discipline on the part of editors, but it saves us an awful lot of trouble too. In this case we can at least take comfort from the small scale of the matter, a change of less than one part in a billion in the conversion between units of values which I suspect have a far greater degree of uncertainty, and of course continue to watch for any RSs on the matter, whether confirming at last what you've found or even (which might well seem improbable) describing how some other aspect of the various consequences of the redefinitions has left the relationship unchanged - but we do have to wait for such publication. NebY (talk) 12:56, 5 June 2026 (UTC)

What I suggest is that we simply add a statement that the change in \mu_0 and the kg has made the value non-exact and leave it at that. That does not qualify as original research.

Unless you object, I will add a sentence to this effect in the last box. Mgolden (talk) 13:34, 5 June 2026 (UTC)

I do object. That statement would not be directly supported by reliable sources, and would differ from reliable sources that show a straightforward 10⁴ relationship. It would breach Wikipedia:No original research.

If you want to take this further, options include WP:3O, WP:DRN, asking at Wikipedia talk:WikiProject Physics (where you're most likely to find editors who follow and can check your workings), or asking at Wikipedia:No original research/Noticeboard (where you're most likely to find editors who'll say whether or not WP:NOR applies). You might find either of the latter two more productive than the first two, in which either a single editor joins the discussion here or a single moderator helps just you and me discuss it in a different venue). NebY (talk) 20:08, 5 June 2026 (UTC)

Before I launch one of those processes I will try one last time to clarify this issue. After reading this, if you tell me you still think there is "original research" here, I will proceed down one of the roads you suggest.

I am by no means making any claim to novelty. This is just an application of something that can be found in virtually any textbook on electromagnetism. (See e.g. Purcell and Morin, Electricity and Magnetism, p 282)

The one and only point I am trying to make is that the value G/T = $10^{-4}$, which used to be exact because of the definitions of the two units, no longer is. As of 2019 it is a measured value.

For the record, the below is the simplest version of the argument. I do not intend to do any calculation involving $\mu _{0}$ since it is not necessary to what I am talking about.

The definition of the gauss is

1 G = $1{\frac {g}{Bi\cdot s^{2}}}$

The definition of the tesla is

1 T = $1{\frac {kg}{A\cdot s^{2}}}$

as shown on their respective pages. The ratio G/T is therefore ${\frac {g}{kg}}{\frac {A}{Bi}}$. Now ${\frac {g}{kg}}$ is just $10^{-3}$.

The definition of the Biot is

The biot is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one centimetre apart in vacuum, would produce between these conductors a force equal to two dynes per centimetre of length.

and the definition of the Ampere is

The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in vacuum, would produce between these conductors a force equal to 2×10−7 newtons per metre of length.

Both of these quotes appear on Wikipedia on the units' respective pages; they're from the official definition documents.

These describe the same experiment but with different dimensions. However, we know how the different sizes play into the resulting definitions of the respective units, and working through the various powers of 10, you can easily derive that 10 A = 1 Bi. Indeed, the ampere was chosen specifically to be 1/10 the emu unit of current (AKA the biot). (There are appropriate references for this on the Ampere_(unit) page.)

This is precisely what is used on the Gauss_(unit) page to derive the ratio 1 G = $10^{-4}$ T.

So far, everything is totally conventional.

The sum total of my point is that as of 2019 the ampere is no longer defined in this way. The ampere is a particular number of electrons per second, without reference to the force between any set of wires. Therefore the ratio of the biot to the ampere is now something that has to be measured, and it's not exactly 10. Therefore, the tesla is approximately but not exactly $10^{4}$ gauss, and it is a value that has error bars.

End of argument. Nothing above is original research.

Now, just to close this off: the reason I brought $\mu _{0}$ is that you requested a value for the conversion factor. When I spoke I forgot that the kg was changed at the same time as the ampere. If the kg had not been changed, then my calculation would work. I am unable to find any estimate of how the kg was changed, so we should make the point without the estimate, which in my view is not particularly interesting given how tiny the correction is.

Please let me know how to proceed from here. Mgolden (talk) 03:00, 6 June 2026 (UTC)

Minor correction. Where I typed "the definition of the ampere is", I should have written "the definition of the ampere WAS". Mgolden (talk) 03:40, 6 June 2026 (UTC)

Whether or not that is "research" from a scientist's POV, it is from Wikipedia's. I do recommend reviewing Wikipedia:No original research: from the first paragraph,

Wikipedia articles must not contain original research. On Wikipedia, original research means material—such as facts, allegations, and ideas—for which no reliable source has ever been published. ... The definition of original research includes any analysis or synthesis of published material that reaches or implies a conclusion not stated by the sources. To demonstrate that one is not adding original research, one must be able to cite – even if not yet expressly cited – reliable, published sources that are directly related to the topic of the article and directly support the material being presented.

I can't tell you how to proceed from here; all I can say is that as long as content would breach WP:NOR, it mustn't be included. I've mentioned some ways you could pursue the matter further, if you think it worthwhile. NebY (talk) 10:49, 6 June 2026 (UTC)

OK, I will proceed. Which point above do you think is original research? Everything except the last paragraph is already on Wikipedia, and the reference for the last paragraph is the announcement from the BIPM (or any one of a number of other places). Mgolden (talk) 14:10, 6 June 2026 (UTC)

Your conclusion "Therefore, the tesla is approximately but not exactly 10⁴ gauss" is not directly supported by RSs, nor would any paraphrase of that be – see the opening of Wikipedia:No original research as quoted above, see Wikipedia:No original research#Synthesis of published material, which begins

Do not synthesize meaning from multiple sources to state or imply a conclusion not explicitly stated by any of those sources. Similarly, do not combine different parts of one source to state or imply a conclusion not explicitly stated by that source.

and its companion Wikipedia:Verifiability, the opening paragraph of which includes

Even if you are sure something is true, it must have been published in a reliable source before you can add it.

If you are considering proceeding, I do recommend first reviewing those policies in full, not just the snippets above; they are fundamental. NebY (talk) 14:35, 6 June 2026 (UTC)

I have reviewed them.

I have posted a notice of our discussion on the Wikipedia talk:WikiProject Physics inviting people to weigh in.

I would point out that we have no RS for the statement 1 T = $10^{4}$ G exactly as applied to the 2019 definitions of those units. As I have explained, we never will find such a statement because it isn't true. The minimum we can do is to note that the information only applies to the 2019 definitions. Mgolden (talk) 15:24, 6 June 2026 (UTC)

I think this discussion is an overkill. A minor amount of simple mathematics is allowed, and does not need an RS.

1. State that prior to 2019 the definition was XYZ with a ref or two
2. State that after 2019 the definition was xyz with a ref or two
3. State, "Thus prior to 2019 1T =..." (three lines maybe better) and "after 2019..". No source is needed here.

Ldm1954 (talk) 16:05, 6 June 2026 (UTC)

The issues of Gaussian to SI conversion with respect to 2019 changes are mentioned in this analysis:

https://physics.byu.edu/faculty/colton/docs/phy441-resources/gaussian-units.pdf

In the Particle Data group table, https://pdg.web.cern.ch/pdg/2020/reviews/rpp2020-rev-phys-constants.pdf, which explicitly says talks about the impact of 2019 changes, the equivalence $1{\textrm {G}}\equiv 10^{-4}{\textrm {T}}$ is given.

Absent explicit discussions of the impact of the 2019 changes on the Tesla unit in sources, I think we should conclude that the changes were not notable. Johnjbarton (talk) 17:14, 6 June 2026 (UTC)

Yes, I had come across that BYU document. From reading it it is clear that it was written under the pre-2019 units and the addendum was added later. Mgolden (talk) 17:51, 6 June 2026 (UTC)

I've only skimmed the discussion above, but I'll give my opinion anyway: We should not attempt to derive the exact conversion between units ourselves. Simple math or not, that would be WP:OR and I've seen well-intentioned efforts like that go wrong before. Per MOS:UNCERTAINTY we do not need to give an exact conversion. We can still say that a Tesla is 10⁴ G. We can say that the relationship is now approximate and explain why. --Srleffler (talk) 17:01, 6 June 2026 (UTC)

The derivation I am quoting is from the Gauss Wikipedia page. I was not planning to derive anything on either the gauss or tesla pages, just to note that the exactness of the relation depends on the definition 1 Bi = 10 A, which is no longer true in the 2019 definition.

A notable thing about that PDG page is that it actually gives a value for $\mu _{0}$ that includes an error bar. Mgolden (talk) 17:46, 6 June 2026 (UTC)

Sorry, forgot to say - yes, what you are suggesting is exactly what I was proposing to do. Mgolden (talk) 17:51, 6 June 2026 (UTC)

Since the above, Gauss (unit) has been edited; interested editors might like to glance at that. — Preceding unsigned comment added by NebY (talk • contribs) 15:49, 7 June 2026 (UTC)

Yes, I edited it as agreed here. There was an agreement that we cannot source a conversion factor, but there is clear agreement above that the affirmative statement that 1 T = 10000 G no longer holds. Mgolden (talk) 17:55, 7 June 2026 (UTC)

The post 2019 PDG source gives the 1 T = 10000 G conversion factor. You think it is obviously incorrect. I'm not convinced. On the contrary I think maintaining the conversion factor at the pre-2019 value makes sense in terms of how Gaussian units are used. Their purpose is convenience in formula manipulations. Convenience, not extreme accuracy, is the goal. I might be wrong, which is why I looked for sources. Lack of sources is also a sign: it means changes in this conversion value is not significant, not encyclopedic. Johnjbarton (talk) 18:21, 7 June 2026 (UTC)

On the PDG pamphlet you cite, the symbol ≘ appears between the G and T values. That symbol means "corresponds to", that is, the two units appear in different unit systems. It implies nothing about whether the conversion is exact or not. It can be exact (as in 1N = 10⁵ dyne, but does not have to be.

It is completely clear from the equation right above that in order for the relationship to be exact, the biot has to be exactly 10 amperes. If you believe that the conversion is exactly 10⁴, you could use the statement that 1 T = 10000 G to derive the relationship between the biot and the ampere. You would get the pre-2019 definition. That definition no longer holds., and I have provided a source (directly from the BIPM) that says that it doesn't. Mgolden (talk) 18:29, 7 June 2026 (UTC)

The PDG source https://pdg.web.cern.ch/pdg/2020/reviews/rpp2020-rev-phys-constants.pdf shows three bars like $\equiv$ meaning as I understand it "equivalent". We can report it as such. "Corresponds to" is also fine by me. Johnjbarton (talk) 18:51, 7 June 2026 (UTC)

If you look at what I wrote, I actually left the correspondence symbol in, and the left the statement that 1 T ≘ 10000 G in place. What I said below is that since the ampere is no longer defined as 1/10 biot, the correspondence is no longer exact. This is exactly what I was asked to do and it should not have been reverted.

In the 2019 redefinition there was a change that made the exact relationship non-exact, by (as discussed above) a very, very small amount. No one who is actually converting units (who is the target audience for the page in the PDG booklet) cares about the difference.

To reiterate, if you believe that 10000 G = 1 T exactly, you can derive the equation $\mu _{0}=4\pi \times 10^{-7}$. The PDG booklet explicitly states that $\mu _{0}$ is not this value. People can rest assured the the people who write the PDG booklet (I knew some of them, back in the day) understand this point. Mgolden (talk) 19:02, 7 June 2026 (UTC)

But I didn't derive that equation, which is exactly the point we are trying to make. We agree that that the PDG is a reliable source. We should report what they say.

Your claims about boit are also unsourced.

There is not an authoritative single source for Gaussian units but according to other sources, this clearly reliable source was widely used:

• Jackson, John (1975), Classical Electrodynamics, 2nd Ed., John Wiley, ISBN 0-471-43132-X

On page 819 Jackson explains on page 821 how to convert Gaussian to MKSA units, closely related to SI. The procedure involved formula unrelated to units of the CGS system like the biot. However, Jackson is criticised in this source:

• Quincey, P. (2024). Simple methods for converting equations between the SI, Heaviside–Lorentz and Gaussian systems. European Journal of Physics, 45(5), 055801.

which gives direct conversions for SI and Gaussian units. The source uses formula, not numerical values, to relate the units. This paper refers to many other sources about conversions. It is these sources that we should attempt to summarize rather than come up with a story about which part of PDG is correct. That is we should report the inconsistency not fix it. Johnjbarton (talk) 19:58, 7 June 2026 (UTC)

I reiterate: the PDG says 1 T ≘ 10000 G. That statement appeared literally in the article as I wrote it. I am happy to cite the PDG booklet and even put in a note that the value in the conversion section gives the value 10000, but the value of $\mu _{0}$ is not $\mu _{0}=4\pi \times 10^{-7}$N⋅A⁻². You are asserting that the PDG intended us to read the ≘ in a particular way, but I don't know how one can assert that.

The statement that the Ampere was defined as 1/10 abampere (aka biot) is given here:

Vacuum_permeability#Systems_of_units_and_historical_origin_of_value_of_μ0

Happy to reiterate that on the Gauss page if need me.

I have cited an RS above (Purcell and Morin) that the ratio of T to G is exactly 10000 in the old SI units. I will happily add that to the references as well, and I can find more if that's insufficient.

Regarding Jackson: he is stating that when the formulas in the book (which uses Gcgs) are transformed using the substitutions he lists, then the formulas are correct for SI. This means that the relationships between the formulas are exact, since he is giving exact values. Of course, since Jackson died in 2016 his book used the old SI units. (In fact, there's a third edition that uses SI, but I don't have a copy of that. If I get a chance I will try to see what he said.)

I don't have access to the Quincy paper. The abstract doesn't say anything that seems to bear on that subject. If you have a link to it please let me know, or I can try to get it from a library.

Let me see if this helps:

Based on what I have seen above, I think we all agree that in the old SI the relationship between T and G was exactly 10000, and this can be backed up by lots of RSs. Based on this, I think we also agree that the equation as in the gauss article (which I have not changed) is exact.

We also agree that the Ampere was changed in 2019, as backed up by the references directly to the BIPM. So the ampere(pre-2019) is defined differently than 1 ampere(2019).

The pre-2019 and 2019 SIs are actually different unit systems. The different definitions imply that ampere(pre-2019) ≘ ampere(2019) - as evidenced that they gave the same name and no conversion factor - but not that the two quantities are exactly identical. Because the 2019 system is better defined than the pre-2019 system (in the sense that the measurements doable in that system are more accurate) it's okay to use ≘ but not =. That is why one does not apply a conversion factor from an old measurement to a new one.

However, since the two units are not defined commensurately ampere(pre-2019) $\neq$ 1 ampere(2019). Therefore, the exactness of the relation 1 Bi = 10 A (which is the only thing at issue here, if you think about it) is no longer true. Mgolden (talk) 21:21, 7 June 2026 (UTC)

I have opened Wikipedia:No_original_research/Noticeboard#Dispute_about_conversion_of_tesla_to_gauss to get an authoritative answer about whether this constitutes original research. Mgolden (talk) 18:22, 7 June 2026 (UTC)

Please see the discussion on the NOR Noticeboard here:

Wikipedia:No_original_research/Noticeboard#Dispute_about_conversion_of_tesla_to_gauss

I believe that what I posted there should resolve this discussion. Mgolden (talk) 02:53, 8 June 2026 (UTC)

Notes

Meaning of correspondence symbol

I see that there have been a number of changes to this page since I last looked at it. In particular, I see that the correspondence symbol has been replaced with the equals sign with the assertion that the symbol was not correct. In fact, a symbol of that type is required when converting units in different systems, and it has been on this page for a long time.

This is what I got from Google's AI when I asked "symbol for correspondence of units in different systems" followed by "What is the symbol that indicates correspondence of two units in different systems"

---

The Correspondence Symbol (≙)

The ≙ symbol (an equal sign with a hat or caret above it) is explicitly used in scientific and engineering notation to show the equality of inherently non-equal things. It is designed specifically for scaling relationships, maps, and conversions across differing systems of measurement where a strict, literal mathematical equality = is technically incorrect because the underlying base units differ.

How it is used: (10 min ≙ 2 kg) or 1 inch ≙ 2.54 cm}

Other Alternative Symbols

Depending on the specific region or scientific field, three other symbols are occasionally substituted to show unit correspondence:

Tilde (~): Used primarily in physics to show that a value or unit in one system is of the same order of magnitude or roughly corresponds to a unit in another system. [1, 2, 3]

Triple Bar (≡): The "identical to" or "defined as" sign, which shows that a unit expression is fundamentally identical across systems by definition. [1, 2, 3, 4]

Corresponds To (≘): An equal sign with an inverted arc/U-shape on top, used interchangeably with ≙ in specific geometric or technical fields to map one domain directly onto another.

---

Note that the references Google gives are

https://math.stackexchange.com/questions/790019/what-is-the-symbol-%E2%89%99-most-commonly-used-for-in-a-mathematical-or-math-related-co

https://www.vedantu.com/question-answer/columni-columnii-columniii-columniv-physical-class-11-physics-cbse-5fd319add6856f7ca918d13a

https://www.pearson.com/channels/intro-to-chemistry/flashcards/topics/conversion-factors-simplified/conversion-factors-simplified-definitions

As always with AI's references, these are 100% valueless, not one of them supports the claim being made (and yes, there were only three distinct ones). But their existence in the result indicates that somewhere out there is something that supports these statements.

---

Note that on Wikipedia the practice seems to be to use ≘ but the PDG used ≡.

I don't want to revert these changes without discussing them first. Mgolden (talk) 20:09, 9 June 2026 (UTC)

(In my experience with AI, one has to ask very pointedly for authoritative, reliable references and sometimes twice).

This source describes how the "corresponds to" should be used, and it is rather limited in scope.

https://ieee-pes.org/wp-content/uploads/2023/01/appendix.pdf

This source writes out "corresponds to" specifically in the case of G to T:

https://www.govinfo.gov/content/pkg/GOVPUB-C13-ff857f3d2d16a5c97f5cd65764a52831/pdf/GOVPUB-C13-ff857f3d2d16a5c97f5cd65764a52831.pdf

Since this symbol is not widely known I wonder how valuable it is for an encyclopedia.

The symbol is defined in "ISO 80000-1: Quantities and units — Part 1: General" but that document requires secret knowledge to read.

https://www.iso.org/obp/ui/en/#iso:std:iso:80000:-1:ed-2:v1:en Johnjbarton (talk) 21:46, 9 June 2026 (UTC)

I tried asking claude for reliable references but it gave me similar crap. My conspiracy theory is that the search engines are deliberately make their web search worse to force people to use their AI to get answers, but I don't have an RS for that.

RefarThis is about as definitive as can be, from NIST:

https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-5-units-outside-si

Section 5.3.1:

CGS units

Table 10. Examples of CGS units with special names (not accepted for use with the SI by this Guide)

...

gauss(c) Gs,G 1 Gs corresponds to 10^-4T

oersted(c) Oe 1 Oe corresponds to (1000/4π) A/m

maxwell(c) Mx 1 Mx corresponds to 10^-8 Wb

...

This in a document that used = everywhere for conversion factors. Note that they did use = for 1 in = 2.54 cm, because that conversion factor is in fact exact. (I assume if we found the pre-2019 version of this document they would have.)

The PDG put was more hardassed about this, and used the Triple Bar for this, even for dynes to newtons, which, unlike gauss to tesla really will never change, precisely to indicate that the SI has deemed them not acceptable.

If you think that it's confusing to lay readers, you can change it to words (or I will if you prefer) but it's not correct to leave it as an equals. Note that I have seen this symbol in other places on wikipedia, so I'd prefer it to be changed back, absent any evidence that it's actually confusing anyone. Mgolden (talk) 22:42, 9 June 2026 (UTC)

@Srleffler removed it in this edit.

I made a change the implements the sourced "corresponds to". It would great if the issue could be discussed with a more complete source. Johnjbarton (talk) 00:08, 10 June 2026 (UTC)

I think a better question is what the agreed Wikipedia style standard is for this. There are lots of articles about units and it would be better for them to follow the same standard.

Given that this is a change you would like to make, I think it's appropriate for you to find the supporting documentation about it, and produce some evidence that people have been confused about what was there. So long as we don't use = here I will not change it. Mgolden (talk) 00:18, 10 June 2026 (UTC)

The change I made is sourced. The source we agree is reliable and it lists other units. Thus the same change could be applied to other units listed for consistency. Johnjbarton (talk) 00:42, 10 June 2026 (UTC)

To make myself clear: I agree your change is sourced. Frankly, it doesn't even need a source IMO. I think it's unnecessary, but I am not talking about reverting it.

I don't know the protocol here. Before I made my original change, I discussed it here. There were five people in the discussion, three of them agreed and I made the change. I now know that I should have worked longer on a consensus.

Here, in this case, making this change will affect a number of articles. The use of the symbol wasn't wrong, and it has been there since Sept 2022, on this commit:

https://en.wikipedia.org/w/index.php?title=Tesla_(unit)&oldid=1117244288

Moreover, since the symbol was introduced right under the words "... is equal to ...". I don't see what the possibility for confusion was. But that's just my opinion, and you're fee to differ.

I do however believe that more people should weigh in before this change is accepted. I don't know what appropriate forum for that is. Do you have any suggestion? Mgolden (talk) 01:35, 10 June 2026 (UTC)

The symbol I removed was "≘" and not "≙". When I wrote that it was the wrong symbol I had mistaken it for "≏". In any event, these variant equals signs are too obscure to use in an encyclopedia article without explanation. At the level of an infobox in a Wikipedia article on a common unit it is not wrong to say that 1 T is equal to 10⁴ G. The distinction between "equals" and "corresponds to" is far too fussy for an infobox. If the article is going to make that distinction at all, it should be in body text not in an infobox. Infoboxes should be simple and self-contained, not rely on specialist knowledge.--Srleffler (talk) 04:04, 10 June 2026 (UTC)

All agreed. The question is now strictly about whether this change is necessary. The justification is that the lay person will be confused.

I bring this up because I was planning to use the symbol in the text of the article, as it was and is still in the Gauss article. Mgolden (talk) 04:57, 10 June 2026 (UTC)

It is an error to use that symbol anywhere on Wikipedia without explaining it. The symbol is so obscure that searching for ≘ on Wikipedia doesn't even take one to an explanation of what it means. "Corresponds to" as used here is an obscure concept, which should be explained or removed everywhere. --Srleffler (talk) 05:33, 10 June 2026 (UTC)

See the discussion on [noticeboard about the change I made to this page]

Yet another round

@Srleffler @Mgolden I rewrote the contended section again, based on the new sources. These sources say nothing about biot. I included what I thought the articles had to say relevant to the tesla. Please review. Johnjbarton (talk) 15:13, 10 June 2026 (UTC)

Leaving out the biot means that nothing has been derived, and the inclusion of the dimensions just repeats what is above. The entire point of that equation is to show where the 10⁴ comes from and why the redefinition of the ampere affects the exactness of the relationship. Moreover, there's now an equals sign there, as opposed to "corresponds to", so it's technically incorrect. Mgolden (talk) 15:26, 10 June 2026 (UTC)

No source provides a derivation. Ergo, no derivation. I removed the equal sign. Johnjbarton (talk) 19:40, 10 June 2026 (UTC)

Thank you for doing that. It is clear that this Wikipedia article need not and should not digress into the relationship between the ampere and the biot. I've tried some slight editing – do please review. NebY (talk) 20:02, 10 June 2026 (UTC)

My correspondence with the Particle Data Group

Below you can see my correspondence with the Particle Data Group at the Lawrence Berkeley Lab. As it turns out, their use of the triple equals sign in the equation for the conversion factor between tesla and gauss was incorrect. My belief, based on that fact, that they were using the triple equals as an alternate version of "corresponds to" was also incorrect.

---

From: PDG PDG <***@lbl.gov>

To: ***

Subject: Re: Question about the conversion constants table

Date: Wednesday, June 17, 2026

Hi ***.

The triple equal sign means that it is by definition .

We believe that your other issue is correct and will check and fix it.

Thank you.

***

On Tue, Jun 16, 2026 *** wrote:

> I have a question about the notation used in the conversion factors section of the 2026 PDG booklet. Here are all the constants. This came up in some editing of a wikipedia article I was involved in.

> 1 in ≡ 0.0254 m

> 1 G ≡ 10^{−4} T

> 1 eV = 1.602 176 634 × 10^{−19} J (exact)

> kT at 300 K = [38.681 727 0718...]^{−1} eV (exact∗)

> 1 Å ≡ 0.1 nm

> 1 dyne ≡ 10^{−5} N

> (1 kg)c2 = 5.609 588 603... × 10^{35} eV (exact∗)

> 0◦C ≡ 273.15 K

> 1 barn ≡ 10^{−28} m^2

> 1 erg ≡ 10^{−7} J

> 1 C = 2.997 924 58 × 10^9 esu

> 1 atmosphere ≡ 760 Torr ≡ 101 325 Pa

> (I hope that the symbols have not been mangled by e-mail.)

> I am wondering about the use of the triple bar AKA "identical to" (https://unicodeplus.com/U+2261) in these formulas. I have seen this symbol used for "corresponds to" when the unit systems are incompatible, though I believe the more common symbol for this is ≘ (https://unicodeplus.com/U+2258). Is that the sense in which it is being used? Another common use for the triple bar is to function as a definition of something.

> Whichever definition I take, I am confused here. An inch is now defined as 0.0254 m, but it is not part of the SI, so maybe the triple bar indicates different systems. The gauss is not in the same unit system _and_ it is not exactly equal to 10^{-4} T (since 2019), so most documents now would tend to use corresponds to, either as a symbol or in words. 1 dyne is exactly 10^{−5} N, but a stickler could say that they're not in the same unit system. The conversion for the coulomb has the exact value of the speed of light, but this is no longer the exact relationship for the coulomb to the esu, so I would not expect an equals sign here.

> Can you explain how the triple bar and equals symbols are being used here?

> Thanks,

> *** Mgolden (talk) 00:12, 18 June 2026 (UTC)

After this conversation, the Particle Data Group has revised their booklet.

https://pdg.lbl.gov/2026/reviews/rpp2026-rev-phys-constants.pdf

The conversion factor from gauss to tesla now reads

$1\mathrm {G} \equiv 10^{-4}\times r_{\mu _{0}}\mathrm {T}$§§

where the footnote §§ is

The ratio $r_{\mu _{0}}\equiv {\sqrt {\mu _{0}/(4\pi \times 10^{-7}\mathrm {N} \mathrm {A} ^{-2})}}$ = 0.999 999 999 93(8). Prior to the 2019 revision of the SI unit system, $\mu _{0}\equiv 4\pi \times 10\mathrm {N} \mathrm {A} ^{-2}$ Mgolden (talk) 05:01, 15 July 2026 (UTC)