How this calculator works
Gallons measure volume and pounds measure mass, so the conversion needs the density of the liquid. Mass is volume times density. Water is about 1,000 kg per cubic metre, which is 1 kg per litre, so a US gallon of water has a mass of about 3.785 kg or 8.345 lb. Milk, fuel, honey and oil all have their own densities, and some vary with temperature and grade. The presets are typical values for those liquids; use the custom density row for a specific measurement or specification.
Formula
cubic metres = gallons x 0.003785411784 for US gallons, or x 0.00454609 for imperial gallons. kilograms = cubic metres x density in kg/m3. pounds = kilograms / 0.45359237. A litre is 0.001 m3.
Worked example
1 US gallon of water is 3.78541 kg or 8.3454 lb. 1 US gallon of honey at 1,420 kg/m3 is 5.37528 kg or 11.8505 lb. 5 L of diesel at 830 kg/m3 is 4.15 kg or 9.14918 lb. An imperial gallon of water is 4.54609 kg or 10.0224 lb.
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Frequently asked questions
Why is the answer different for different liquids?
A gallon is a volume, and the same volume holds different masses of different liquids. Honey is much denser than gasoline, so a gallon of honey weighs substantially more than a gallon of gasoline.
How accurate are the preset densities?
They are typical values for the named liquid. Fuel density changes with grade and temperature, milk changes with fat content, and honey depends on moisture. For a precise result, enter a measured density in the custom row.
What is the density of water exactly?
Water reaches its maximum density of about 999.97 kg/m3 at about 4 degrees Celsius. The preset rounds that to 1,000 kg/m3. At room temperature the density is closer to 997 kg/m3, a difference of about 0.3 per cent.
Does this use US or imperial gallons?
Both are offered in the unit selector, along with litres. The gallon choice changes the volume, and the liquid choice changes the density, so check both before reading the mass.