A4

A4 commonly refers to:

A4 paper, a paper size defined by the ISO 216 standard, measuring 210 mm × 297 mm (8.27 in × 11.7 in)

A4 and variants may also refer to:

Arts and media

A4 or A₄, the musical note La or A in the fourth octave
A440 (pitch standard), the use of the musical note A to reference musical pitch
A4, a 1981 component for the Scourge of the Slave Lord adventure in the Dungeons and Dragons role playing game
Vlad A4, Belarusian YouTuber

A4, the designation for air force headquarters in the NATO continental staff system concerned with logistics
- A4 Air Logistics, a branch of the Joint Force Air Component Headquarters in the UK
A 4; see List of Swedish regiments for A4, a Swedish designation (4th Artillery Regiment) that has been used by:
Gotland Artillery Regiment (designation: A 4), until 1892
Norrland Artillery Regiment (designation: A 4), 1893–1997

ATC code A04 Antiemetics and antinauseants, a subgroup of the Anatomical Therapeutic Chemical Classification System
Lipoxin A4, a lipoxin
Androstenedione, an androgen steroid hormone
Combretastatin A-4, a stilbenoid chemical compound
Subfamily A4, a rhodopsin-like receptors subfamily

British NVC community A4 (Hydrocharis morsus-ranae - Stratiotes aloides community), one type of Aquatic communities in the British National Vegetation Classification system
A₄, the alternating group on four elements
A4, a type of stainless steel
Lely (company) Astronaut A4, the fourth version of the Astronaut robot manufactured by Lely
Zeolite A-4, a sodium-type molecular sieve also known as 4A
M16A4, a variant of the American M16 rifle

A-4 Helldiver, the civil version of the Curtiss Falcon an attack aircraft manufactured by Curtiss Aircraft Company
Douglas A-4 Skyhawk, a 1954 attack aircraft manufactured by Douglas Aircraft Company
Breda A.4, a 1926 Italian biplane trainer aircraft
Aggregat-4, the technical name for V-2 ballistic missile
Southern Winds Airlines (IATA code: A4), a defunct Argentine airline
Azimuth (airline) (IATA code: A4), a Russian airline
A-004, the sixth and final abort test of the Apollo spacecraft
SPAD S.A-4, 1915 French reconnaissance fighter built by SPAD

USS A-4 (SS-5), a Plunger-class submarine of the US Navy
HMNZS Kahu (A04), a 1978 Royal New Zealand Navy Moa-class inshore patrol vessel
HMS A4, an A-class submarine of the Royal Navy
Belgian ship A4, a Belgian naval patrol vessel of World War II

Audi A4, a luxury compact executive car manufactured by Audi, introduced in 1994
Arrows A4, a 1982 British racing car
Prussian A 4, a Prussian railbus
Leopard 1A4, a variant of the German Leopard 1 main battle tank
Leopard 2A4, a variant of the German Leopard 2 main battle tank

A4 paper, a paper size defined by the ISO 216 standard, measuring 210 mm × 297 mm (8.27 in × 11.7 in)
A4 (classification), an amputee sport classification
Réti Opening (Encyclopaedia of Chess Openings code: A04)
A4, a climbing route grade
In town and country planning in the UK, code A4, permission to use specific land or premises for pubs and bars
A4 pod, a family of killer whales living in British Columbia coastal waters
Biu-Mandara A.4 languages, a family of languages spoken in Cameroon and Nigeria
A4 Revolution, the 2022 COVID-19 protests in China
Assembly Four, an Australian computer technology company which operated Switter