A4 M4 (Sydney)

A4 most often refers to:
* A4 paper, a paper size defined by the ISO 216 standard, measuring 210 × 297 mm

A4 and variants may also refer to:

Science and mathematics

* British NVC community A4 (''Hydrocharis morsus-ranae - Stratiotes aloides'' community), one type of Aquatic communities in the British National Vegetation Classification system
* Combretastatin A-4, a stilbenoid chemical compound
* ''A''₄, the alternating group on four elements
* A4, a type of stainless steel, as defined by ISO 3506, equivalent to SAE steel grade 316L
* Subfamily A4, a rhodopsin-like receptors subfamily

Medicine

* ATC code A04 ''Antiemetics and antinauseants'', a subgroup of the Anatomical Therapeutic Chemical Classification System
* Lipoxin A4, a lipoxin
* Androstenedione, an androgen steroid hormone

Transportation

Aeronautics and astronautics

* "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
* A4, Southern Winds Airlines, the defunct Argentine airline, as its IATA code
* A4, Azimuth (airline), as its current IATA code
* A-004, the sixth and final abort test of the Apollo spacecraft
* S.A-4 or A.4, 1915 French reconnaissance fighter built by SPAD

Railways

* Bavarian A IV, an 1852 German steam locomotive model
* LNER Class A4, a class of steam locomotives, including the famous ''Mallard''
* PRR A4, an American Pennsylvania Railroad locomotive classification
* Togoshi Station, number A-04 on the Toei Asakusa Line

Ships

* ''A-4'', , a ''Plunger''-class submarine of the United States Navy, which was renamed ''A-4'' on 17 November 1911
* , a 1978 Royal New Zealand Navy ''Moa''-class inshore patrol vessel
* , an A-class submarine of the Royal Navy
* , a Belgian naval patrol vessel of World War II

Other vehicles

* Audi A4, a luxury compact executive car manufactured by Audi, introduced in 1994
* Arrows A4, a 1982 British racing car
* Prussian A 4, a 1913 German railbus

Roads and routes

* List of A4 roads
* A4, a Metrobus route in Washington, D.C.

Military

* A4, the model number of the World War II-era German V-2 rocket
* A4, the designation for air force headquarters in the NATO continental staff system concerned with logistics
** In the United Kingdom, the A4 Air Logistics branch of the Joint Force Air Component Headquarters
* A 4, see List of Swedish regiments for A4, a Swedish designation (4th Artillery Regiment) that has been used by:
** Gotlands artilleriregemente (unknown–1892)
** Norrlands artilleriregemente (1893–1997)
* Douglas A-4 Skyhawk, an American attack aircraft introduced in 1956
* M16A4, a variant of the American M16 rifle
* Leopard 1A4, a variant of the German Leopard 1 main battle tank
* Leopard 2A4, a variant of the German Leopard 2 main battle tank

Computing

* Apple A4, a microprocessor used in some Apple products
* AMD A4, a microprocessor
* Samsung Galaxy A04, a smartphone manufactured by Samsung Electronics

Other uses

* A4 (classification), an amputee sport classification
* 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
* A04, Encyclopaedia of Chess Openings code for Réti Opening
* A4, a grade (climbing)
* A4, the code for permission to use specific land or premises for pubs and bars in town and country planning in the UK
* A4 Pod, a family of killer whales living in British Columbia coastal waters
* A4, a 1981 component for the ''Scourge of the Slave Lord'' adventure in the ''Dungeons and Dragons'' role playing game
* Biu-Mandara A.4 languages, a family of languages spoken in Cameroon and Nigeria

See also

* 4A (disambiguation)
* A4A (disambiguation)
* AIV (disambiguation)
{{Letter-Number Combination Disambiguation