Volume Converter

How to use this calculator#

1. 1
   Establish which system the figure came fromUS customary and UK imperial share every unit name below the litre but almost none of the sizes. A recipe, a fuel figure or a drinks measure quoted in 'pints' or 'gallons' is meaningless until you know which side of the Atlantic wrote it.
2. 2
   Enter the value and pick the matching unitThe unit list separates the two systems explicitly — US fluid ounce, US pint and US gallon are distinct entries from imperial fluid ounce, imperial pint and imperial gallon. Choose the labelled one rather than the generic name.
3. 3
   Convert dry goods by weight insteadVolume only describes liquids reliably. A cup of a dry ingredient varies with how tightly it is packed, so weigh flour, sugar and grains rather than converting their volume.
4. 4
   Watch the scale of the unit you land on1 m³ is 1,000 litres and 1 cubic foot is 28.317 litres. Reading a cubic-metre figure as if it were litres inflates a result a thousandfold — the classic error in tank, pool and excavation sums.

The formula#

US and imperial gallons are not the same#

The single biggest trap in volume conversion is that the US and imperial systems share unit names but not unit sizes. A US gallon is 3.785411784 litres, while the imperial gallon used in the UK is 4.54609 litres — roughly 20% larger. The pint splits the same way, at 473.18 ml in the US against 568.26 ml in Britain, which is why a British pint of beer looks bigger.

The core factors: 1 litre = 33.814 US fl oz = 0.264172 US gallons; 1 US gallon = 3.78541 L = 4 quarts = 8 pints = 128 fl oz; 1 US cup = 236.588 ml; 1 US tablespoon = 14.7868 ml; 1 US teaspoon = 4.92892 ml; and 1 cubic foot = 28.3168 L. One cubic metre is exactly 1,000 litres, which makes metric volume arithmetic pleasantly simple.

Fluid ounces and everyday amounts#

US and imperial fluid ounces differ too, though less dramatically: 29.5735 ml against 28.4131 ml. That difference is why a US pint holds 16 fluid ounces but an imperial pint holds 20. In practical terms, a 500 ml water bottle is 16.9 US fl oz, a 2 L bottle is 67.6 US fl oz or 0.53 US gallons, and a 330 ml can is 11.2 US fl oz.

Fuel figures catch people out for the same reason. A car rated at 40 miles per US gallon achieves 48 miles per imperial gallon, purely because the imperial gallon holds more fuel. Litres per 100 km inverts the relationship altogether, so it cannot be converted with a single multiplier — always confirm which gallon a published economy figure refers to before comparing.

Measuring volume accurately#

The litre is not strictly an SI unit — the SI unit of volume is the cubic metre — but it is accepted for use alongside SI and defined as exactly one cubic decimetre, meaning 1,000 cubic centimetres. That is why 1 ml and 1 cm3 are identical quantities, and why a millilitre of pure water weighs almost exactly one gram at 4 degrees Celsius.

For liquids, read a measuring jug at eye level from the bottom of the meniscus; parallax alone can introduce a 5% error at small volumes. For dry ingredients, volume is unreliable in principle, because packing density varies — scooping flour rather than spooning it into a cup can add 20% more by weight. Weigh dry goods whenever the recipe or formulation needs precision.

Worked examples#

Reference tables#

Common mistakes#

• Using the imperial gallon where the US gallon was meantThe imperial gallon is 20.1% larger. Price 500 US gallons of fuel using imperial-sized gallons and you under-order by about 100 gallons; convert a 35 UK mpg economy figure straight to US prices and you understate the fuel bill by roughly a sixth.
• Converting a volume with a linear factor1 m = 3.28084 ft, but 1 m³ = 35.3147 ft³ — the factor cubed. Someone converting 10 m³ of concrete as if it were a length gets 32.8 ft³ instead of 353.1 ft³, an order-of-magnitude under-order on a pour.
• Assuming every 'cup' is 236.588 mLThe US customary cup is 236.588 mL, the metric cup used in Australia and New Zealand is exactly 250 mL, the US nutrition-labelling cup is rounded to 240 mL, and Japanese recipes use a 200 mL cup. Across a recipe using five cups of liquid that spread is nearly a third of a cup of drift.
• Measuring dry ingredients by volume and calling it preciseScooping flour from the bag compacts it, and a cup can weigh anywhere from 120 g to 150 g depending on technique. That is a 25% swing in a recipe that specified one number. Volume works for liquids; weigh solids.

Frequently asked questions#

Key terms#

Litre

Exactly one cubic decimetre (1,000 cm³). Not itself an SI unit — the SI unit of volume is the cubic metre — but accepted for use with SI and standard for everyday liquid measure worldwide.

US liquid gallon

Exactly 231 cubic inches, which works out to 3.785411784 L. It is divided into 4 quarts, 8 pints or 128 US fluid ounces. There is also a separate, larger US dry gallon used for produce.

Imperial gallon

Exactly 4.54609 L, originally defined as the volume of 10 pounds of water. Divided into 4 quarts, 8 pints or 160 imperial fluid ounces, and still used for fuel economy figures in the UK.

Fluid ounce

A unit of volume, not weight, despite the shared name with the weight ounce. US: 29.5735 mL. Imperial: 28.4131 mL. Only for water does one fluid ounce weigh roughly one ounce.

Meniscus

The curved surface a liquid forms in a narrow container. Read a measuring jug or cylinder at eye level from the bottom of the curve; reading from above can introduce a 5% error at small volumes.

Cubic metre

The SI unit of volume, equal to exactly 1,000 litres or 35.3147 cubic feet. Used for concrete, excavation, water supply and freight, where litres would produce unwieldy numbers.

Sources#