The British standard ordnance weights and measurements for the artillery were established by the Master General of Ordnance in 1764, and these were not altered until 1919 when the metric system was additionally introduced.

This system has largely been replaced by a calibre system, which is the standard today for most weapon systems in use by the World's armed forces

Armed forces

The armed forces of a country are its government-sponsored defense, fighting forces, and organizations. They exist to further the foreign and domestic policies of their governing body, and to defend that body and the nation it represents from external aggressors. In some countries paramilitary...

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The 18th century standards were based on projectile weight, and dated back to use of muzzle loaded cannons which fired solid cannonballs

Round shot

Round shot is a solid projectile without explosive charge, fired from a cannon. As the name implies, round shot is spherical; its diameter is slightly less than the bore of the gun it is fired from.Round shot was made in early times from dressed stone, but by the 17th century, from iron...

. The designations bore only an approximate relationship to the actual weight of the projectile when it was applied to modern artillery.

The table below lists the metric and Imperial calibres of various British weapons, which utilised the standard after 1919:

Name	Type	Calibre
		Metric	Imperial
1 pounder "pom pom" QF 1 pounder pom-pom The QF 1 pounder, universally known as the pom-pom, was an early 37 mm British autocannon. It was used by several countries initially as an infantry gun and later as a light anti-aircraft gun. The name comes from the sound it makes when firing....	Infantry gun/AA gun	37 mm	1.457 inch
2 pounder Ordnance QF 2 pounder The Ordnance QF 2-pounder was a British anti-tank and vehicle-mounted gun, employed in the Second World War. It was actively used in the Battle of France, and during the North Africa campaign...	Anti-tank gun	40 mm	1.57 inch
QF 2 pounder naval gun QF 2 pounder naval gun The 2-pounder gun, officially designated the QF 2-pounder and universally known as the pom-pom, was a 1.575 inch British autocannon, used famously as an anti-aircraft gun by the Royal Navy. The name came from the sound that the original models make when firing...	Anti-aircraft gun	40 mm	1.575
3 pounder Ordnance QF 3 pounder Vickers The Ordnance QF 3 pounder Vickers was a British artillery piece first tested in Britain in 1910. It was used on Royal Navy warships. It was more powerful than and unrelated to the older QF 3 pounder Hotchkiss, with a propellant charge approximately twice as large, but it initially fired the same...	Naval gun	47 mm	1.85 inch
6 pounder Ordnance QF 6 pounder The Ordnance Quick-Firing 6-pounder 7 cwt, or just 6 pounder, was a British 57 mm gun, their primary anti-tank gun during the middle of World War II, as well as the main armament for a number of armoured fighting vehicles...	Anti-tank gun	57 mm	2.24 inch
BL 10 pounder Mountain Gun BL 10 pounder Mountain Gun The Ordnance BL 10 pounder mountain gun was developed as a BL successor to the RML 2.5 inch screw gun which was outclassed in the Second Boer War.-History:...	Mountain gun	70 mm	2.75 inch
12 pounder	Light field gun	76.2 mm	3 inch
13 pounder	Light field gun	76.2 mm	3 inch
15 pounder	Field gun	76.2 mm	3 inch
17 pounder	Anti-tank gun	76.2 mm	3 inch
18 pounder	Field gun	84 mm	3.33 inch
Ordnance QF 20 pounder Ordnance QF 20 pounder The Ordnance QF 20 pounder was a British 84 mm tank gun introduced in 1948 and used in the Centurion tank and the Charioteer tank destroyer...	Tank gun	84 mm	3.33 inch
25 pounder Ordnance QF 25 pounder The Ordnance QF 25 pounder, or more simply, 25-pounder or 25-pdr, was introduced into service just before World War II, during which it served as the major British field gun/howitzer. It was considered by many to be the best field artillery piece of the war, combining high rates of fire with a...	Gun-howitzer	87.6 mm	3.45 inch
Ordnance QF 32 pounder Ordnance QF 32 pounder The Ordnance QF 32 pounder or ' was a British 94 mm gun, developed as a replacement for the Ordnance QF 17 pounder anti tank and tank gun....	Tank gun	96 mm
60 pounder 60 pounder The British Ordnance BL 60-pounder was a 5 inch heavy field gun designed in 1903-05 to provide a new capability that had been partially met by the interim QF 4.7 inch Gun. It was designed for both horse draft and mechanical traction and served throughout the First World War in the main...	Heavy field gun	127 mm	5 inch