A4 Explained
A4 commonly 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 technology
Computing
Medicine
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
- 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
Railways
Ships
- USS A-4 (SS-5), a Plunger-class submarine of the United States 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
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 Prussian railbus
Roads and routes
Military
- A4, the designation for air force headquarters in the NATO continental staff system concerned with logistics
- 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
- 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
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
- Réti Opening (Encyclopaedia of Chess Openings code: A04)
- A4, a climbing route grade
- 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
- Vlad A4, Belarusian YouTuber
- A4 Revolution, the 2022 COVID-19 protests in China
See also