Volume Converter
Convert between litres, gallons, cups, millilitres and other units of volume, with US and imperial measures kept separate.
How to use this calculator
- 1Enter the value you want to convert.
- 2Pick the unit you are converting from and the one you want.
- 3The table below shows the same value in every other supported unit.
How the calculation works
result = (value × factor(from) ) / factor(to)- factor
- How many litres one unit represents
Every value is converted to litres first, then out to the target unit. This means n units need n factors rather than n² conversion pairs.
US and imperial units of the same name are different sizes. A US gallon is 3.785 L and an imperial gallon 4.546 L — a 20% difference that matters for fuel economy and recipes alike.
Cooking measures are the worst offenders: a US cup is 236.6 ml, an imperial cup 284.1 ml, and a metric cup 250 ml.
Worked example
10 litres to gallons (us)
- 1.One litre is 1 litres, so 10 L is 10 litres.
- 2.One gallons (us) is 3.7854118 litres, so divide: 10 ÷ 3.7854118 = 2.6417205.
- 3.Put another way, 1 L = 0.2641721 gal.
Result: 2.6417205 gal
What volume measures
Volume is the amount of three-dimensional space something occupies — how much a container can hold, or how much liquid, gas or granular material fills it. Because it is length cubed, small differences in a linear measurement compound quickly: a container that is 10% longer, wider and taller than another holds roughly 33% more, not 10% more, which is why volume estimates by eye are so often wrong.
The metric unit is the litre, defined as exactly one thousandth of a cubic metre. It sits comfortably between the millilitre used for small quantities like a dose of medicine and the cubic metre used for things like a room's air volume or a shipping container's capacity.
Metric, US, and imperial — three separate sets of measures
Volume conversion has an extra trap that length and weight mostly avoid: units with the same name mean different amounts depending on which country's system you're in.
- Metric — litres and millilitres, scaled by powers of ten, with no separate "liquid" and "dry" versions. Used worldwide, including for fuel prices, beverage sizes and recipes outside the US.
- US customary — teaspoons, tablespoons, fluid ounces, cups, pints, quarts and gallons — the standard for American cooking, beverage sizes and fuel. A US gallon is defined from the older English wine gallon.
- Imperial (UK) — fluid ounces, pints and gallons that share their names with the US units but are sized differently, because the UK later standardised its gallon on a different historical reference (the volume of ten pounds of water) than the one the American colonies had already inherited.
Why a US gallon and a UK gallon are not the same thing
Both countries started from English units, but the United Kingdom overhauled and unified its system of weights and measures in 1824, redefining the imperial gallon on a cleaner, water-based standard. The United States had already broken away politically by then and kept using the older gallon definition that the British themselves later replaced. The result is that a US gallon (3.785 L) is about 17% smaller than an imperial gallon (4.546 L) — the two countries diverged, and neither one is "wrong," they simply never reconciled the split.
That same divergence carries down to pints and fluid ounces, which is why a "pint" of beer, a recipe's "cup," and a car's fuel economy figures do not translate directly between American and British sources without knowing which gallon is meant.
Common conversion pitfalls
Volume conversions cause more everyday mistakes than almost any other unit type, mostly for these reasons.
- US vs imperial units of the same name — a US cup, pint, quart or gallon is smaller than its imperial namesake by roughly 17-20% — always check which system a recipe or spec sheet is using before converting.
- Volume is not weight — a cup of flour and a cup of water have very different masses; converting a recipe between volume and weight units requires knowing the ingredient's density, not just a unit factor.
- Dry vs liquid measure in the US — the US historically had separate dry and liquid measurement systems for pints and quarts; this converter uses the liquid (fluid) versions, which are what nearly all modern US recipes and containers use.
- Cubic units vs named units — cubic feet, cubic metres and litres describe the same kind of quantity as gallons and cups but are usually reserved for larger volumes — shipping, construction, appliance capacity — rather than kitchen measures.
What this assumes, and where it stops
Assumptions
- Conversion factors follow the internationally agreed definitions of each unit.
Limitations
- Results are computed in double-precision floating point, which is exact to about 15 significant figures.
- Very large or very small values are displayed in scientific notation to avoid misleading precision.
Common questions
Is a US gallon the same as a UK gallon?
No. A US gallon is 3.785 litres; an imperial (UK) gallon is 4.546 litres — about 20% larger. This is why US and UK miles-per-gallon figures are not directly comparable, and why fuel prices per gallon look different between the two.
How many ml in a cup?
It depends which cup. A US legal cup is 240 ml, a US customary cup 236.6 ml, an imperial cup 284.1 ml, and a metric cup exactly 250 ml. This converter uses the US customary cup. For baking, weight is far more reliable than volume.
Sources
- NIST Handbook 44 — units and conversions — US NIST
Formula and content last reviewed on .
Results are estimates for information only, not professional advice.
Related calculators
Tools people commonly use alongside the volume converter.