Volume Converter
Metric, US customary, and UK Imperial units — kept separate on purpose, since a "gallon" isn't the same size in every country.
Common conversions
Volume unit reference
What 1 liter equals in every other unit.
| Unit | Value |
|---|
Why a US gallon and a UK gallon aren't the same size
Unlike length or weight — where an inch or a pound means the same thing whether you call it "imperial" or "US customary" — volume is where the two systems genuinely disagree. A UK (Imperial) gallon is about 20% larger than a US gallon — 4.546 liters versus 3.785 liters. The same roughly-20% gap carries through to pints and quarts too, which is the real reason a British pint of beer is famously bigger than an American one: it isn't a myth or a rounding difference, the Imperial pint (568 mL) genuinely holds about 95 mL more than the US pint (473 mL).
The fluid ounce, though, does the opposite — and this is the detail most conversion charts miss. Even though the Imperial gallon is bigger overall, it's traditionally divided into 160 fluid ounces, while the US gallon is divided into only 128. Slicing a bigger gallon into more pieces makes each individual piece smaller: a US fluid ounce (29.57 mL) is actually about 4% larger than a UK fluid ounce (28.41 mL), even though every larger US volume unit is smaller than its UK counterpart. It's a genuine inversion, not a typo.
One more difference worth knowing if you're following a British recipe: there's no standard "UK cup" here on purpose. British recipes conventionally measure ingredients by weight (grams), not cup volume, so a UK cup isn't a standardized unit the way the US cup is — if a UK recipe does mention a cup, it's worth checking what that particular source means by it rather than assuming it matches the US definition.