How Many Milliliters in a Gallon?

A US gallon holds exactly 3,785.411784 milliliters (millilitres). Multiply the gallons by that number, or by 3,785 for everyday work, since the digits after the decimal point make no practical difference in a kitchen or garage.

The smaller US measures are simple fractions of a gallon. A quart, one fourth of it, is 946.4 ml; a pint, one eighth, is 473.2 ml; and a cup, one sixteenth, is 236.6 ml.

Big results are easier to read as liters. Two and a half gallons, for instance, are 9,464 ml, which is simpler to write as 9.464 L.

In Britain the word gallon means the imperial gallon, which holds 4,546 ml. That is 1.201 gallons in US measure, so a British figure given per gallon spreads over more water.

Check which gallon a guide uses before you mix anything by the gallon. A ratio meant for the imperial gallon comes out stronger if you mix it into a US gallon, because the US jug is smaller.

Directions for concentrates, plant food or pond treatments may give an amount per gallon when you only want a small batch. Work out what share of a gallon you are making, then scale the amount by that share.

A 500 ml spray bottle is 0.1321 of a US gallon, and a 1 L jug is 0.2642 of one. At 4 tbsp per gallon, the liter jug needs 0.2642 × 4 = 1.057 tablespoons.

Measure small amounts like that with spoons or a syringe marked in ml rather than by eye. The gallons to cups converter helps with the bigger shares.