How many litres are in a US gallon?

3.785411784 litres exactly, because the US gallon is defined as exactly 231 cubic inches. The UK imperial gallon is different, at 4.54609 litres.

How many cups in a litre?

4.227 US cups. If a recipe uses metric cups of 250 ml, it is exactly 4.

Volume Converter

Convert between millilitres, litres, teaspoons, cups, pints, quarts, gallons and cubic units.

Draft — figures checked, awaiting an editorial read. Not indexed.

Result—

Formula: Result = amount × (factor of source unit ÷ factor of target unit), with every factor expressed in litres.

What this calculates

This converts volume across metric units, US liquid measures and the cubic units used in construction. It handles the awkward cases in the middle — cubic feet to gallons, millilitres to teaspoons — that come up constantly and that almost nobody remembers. All the US measures here are the liquid ones: the US also has a separate dry pint and dry quart that are about 16% larger, used mainly for produce, and they are not included because mixing them in silently would cause more errors than it prevents.

How it works

Each unit has a factor in litres. The US gallon is defined as exactly 231 cubic inches, which works out to 3.785411784 litres, and every smaller US liquid measure is a clean fraction of it: a quart is a quarter gallon, a pint half a quart, a cup half a pint, a fluid ounce an eighth of a cup, a tablespoon half a fluid ounce, a teaspoon a third of a tablespoon. Cubic feet and cubic inches derive from the exact inch, so those are exact too.

Worked example

A 40 gallon water heater in litres: 40 × 3.785411784 = 151.4 litres. Going the other way, a 2 litre bottle is 2 ÷ 3.785411784 = 0.528 gallons, or 67.6 fluid ounces. A useful one for construction: one cubic foot holds 28.3168 litres, or about 7.48 US gallons — which is why a 55 gallon drum takes up roughly 7.35 cubic feet of floor space.

Common mistakes

Using UK and US measures interchangeably. A UK pint is 568 ml against the US 473 ml, a 20% difference, and the UK gallon is 4.546 litres against 3.785. Recipes and drink measures cross this boundary constantly. Second, confusing fluid ounces with ounces of mass. Third, assuming a US cup is 250 ml — that is the metric cup used in Australia and New Zealand; the US cup is 236.6 ml.

Common questions

How many litres are in a US gallon?: 3.785411784 litres exactly, because the US gallon is defined as exactly 231 cubic inches. The UK imperial gallon is different, at 4.54609 litres.
How many cups in a litre?: 4.227 US cups. If a recipe uses metric cups of 250 ml, it is exactly 4.