25 mm caliber is a range of autocannon ammunition. It includes the NATO standardized Swiss 25×137mm, the Swiss 25×184mm, the Soviet 25x218mmSR, and the Chinese 25×183mmB.

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The 25 mm round can be used for anti-materiel or anti-personnel purposes. In the anti-personnel role, a 25 mm weapon armed with HE rounds can kill large numbers of opposing troops either in the open or in light fortifications. In the anti-materiel role, a 25 mm weapon armed with armor-piercing rounds can disable many types of aircraft and ground vehicles, including some main battle tanks.

The US military uses 25 mm weapons in their AV-8B Harrier, AC-130 gunship, M2 Bradley, LAV-25, F-35 Lightning II and as a standard ship-based munition in the Mk 38 autocannon.

Several sub-types of the NATO 25 mm ammunition are available—the most common being armor-piercing, high-explosive, sabot, tracer, and practice rounds. Cartridges are usually composed of a combination of the aforementioned categories. For example, the M791 is an armor-piercing discarding sabot with tracer (APDS-T) round. It is used against lightly armored vehicles, self-propelled artillery, and aerial targets such as helicopters and slow-moving fixed-wing aircraft.

• 14.5×114mm
• 20 mm caliber
• 23 mm caliber
• 25 mm grenade
• 30 mm caliber
• List of cartridges (weaponry), pistol and rifle

• U.S. Army Field Manual 3-22.1

• Federation of American Scientists: 25mm Ammunition
• UXO Safety Information^{[permanent dead link]}