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Metric Units

SI metric volume units are defined in terms of the cube of a length unit, for example the cubic metre is the volume of a cube with sides 1 metre in length. The litre is another metric volume unit, most commonly associated with liquid volumes, that is accepted for use with SI metric units, due to it being one of the original metric units of the 1795 French system.

Other metric prefixes may be used with the litre, for instance kilolitre, some of which are in common usage. For example the millilitre, often used on medicine spoons, and the centilitre on drinks labels.

Table of Metric Volume Units

Unit As cu m Useful Information
cu cm 0.000001
cu m 1
millilitre 0.000001 Often seen on medicine spoons and in dosages.
centilitre 0.00001 Often seen in drinks labeling.
litre 0.001 Used for volumes of liquids.
Imperial Units

Imperial volume units, as per their metric counterparts, often expressed as a cube of the corresponding length unit. Cubic inches, cubic feet and cubic yards all fit this pattern. There are also some imperial volume units that are not associated with length units, mainly the liquid volume units gallons, quarts, pints and fluid ounces.

Just to make things more complicated there are differences between British imperial liquid volume units and US customary liquid volume units. The British gallon having been defined in 1824 as as the volume of 10 pounds of distilled water weighed in air with brass weights at a barometer reading 30 inches of mercury at a temperature of 62 °F and the US liquid gallon being defined as 231 cubic inches.

Comparing the two one UK gallon = 1.2009499 US gallons, other liquid volumes in both systems are based on the gallon. However it should be noted that there are 20 imperial fluid ounces in the imperial pint and only 16 US customary fluid ounces in a US pint. This makes the imperial fluid ounce and the US fluid ounce very similar in size.

Table of Imperial Volume Units (Cubic Lengths)

Unit As cu m Useful Information
cu in 0.000016387064 Often used for engine capacities in the US
cu ft 0.028316846592 Used for gas and water billing in the US
cu yd 0.764554857984


Table of British Imperial Liquid Volume Units

Unit As litres Useful Information
Fluid Ounce 0.0284130625 1/20th of a British pint
Pint 0.56826125 Still in day to day use for beer and milk
Quart 1.1365225 2 pints or ¼ gallon
Gallon 4.54609


Table of US Customary Liquid Volume Units

Unit As litres Useful Information
Fluid Ounce 0.0295735295625 1/16th of a US pint
Pint 0.473176473 The US pint is smaller than the British pint
Quart 0.946352946 2 pints or ¼ gallon
Gallon 3.785411784 Defined as 231 cubic inches


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