How this calculator works
A US gallon is exactly 3.785411784 L, or 0.003785411784 m3, and an imperial gallon is 4.54609 L. A gram is one thousandth of a kilogram. Converting gallons to grams multiplies the volume by the liquid density in kilograms per cubic metre and then by 1,000 to reach grams. One US gallon of water is 3,785.41 g, but the same gallon of honey is about 5,375 g because honey is 1.42 times as dense. The preset densities are typical values, so use the custom density when a label or a hydrometer reading is available.
Formula
grams = gallons x 0.003785411784 m3 x density in kg/m3 x 1,000 g/kg. For imperial gallons use 0.00454609 m3 instead. Gallons = grams / (1,000 x density x volume factor).
Worked example
1 US gal of water at 1,000 kg/m3 is 3,785.41 g. 1 US gal of milk at 1,030 kg/m3 is 3,899.97 g. 1 US gal of honey at 1,420 kg/m3 is 5,375.28 g. 5 US gal of diesel at 830 kg/m3 is 15,709 g, or 15.71 kg.
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Frequently asked questions
How many grams are in a gallon of water?
A US gallon of water is 3,785.41 g at about 1,000 kg/m3, which is 3.785 kg. An imperial gallon of water is 4,546.09 g.
Why does the answer depend on the liquid?
A gallon is a volume and a gram is a mass. Litre for litre, heavy liquids such as honey contain more mass than light liquids such as gasoline, so the same gallon weighs different amounts.
Is a US gallon or an imperial gallon used?
Both are available. The US gallon is 3.785411784 L and the imperial gallon is 4.54609 L, so an imperial gallon holds about 20 per cent more liquid and gives a larger gram answer for the same density.
How exact are the preset densities?
They are typical room temperature values. Fuel densities in particular move with temperature and blend, so treat a preset fuel figure as an estimate and enter the supplier value for a precise answer.