Gallons to Grams Calculator — Convert by Liquid Density
Convert a volume in US or Imperial gallons to mass in grams (and kg, oz, lb) by selecting the substance from the preset list — water, milk, oil, fuel and more — or entering a custom density.
gal
Gallon type
Substance
Grams = Volume (mL) × Density (g/mL) • gallons → mL using exact statutory factor
- 1
Millilitres per gallon
3,785.41Statutory definition: 1 US liquid gallon = 3785.41 mL. - 2
Volume in millilitres
1 × 3,785.41 = 3,785.41 - 3
Mass in grams
3,785.41 × 1 g/mL = 3,785.412
How does this calculator work?
Grams = Gallons × (mL per gallon) × Density (g/mL). US: 1 gal = 3,785 mL so 1 US gal of water ≈ 3,785 g ≈ 8.34 lb. Imperial: 1 gal = 4,546 mL so 1 Imp gal of water ≈ 4,546 g ≈ 10.02 lb. Gasoline (~0.737 g/mL): 1 US gal ≈ 2,790 g ≈ 6.15 lb.
Formula
How this is calculated
A gallon is a unit of volume; a gram is a unit of mass. To convert between them you need the liquid's density — how many grams are packed into each millilitre (or cubic centimetre). The approach is: (1) convert gallons to millilitres using the exact statutory definition of the chosen gallon type, then (2) multiply by density (g/mL) to get grams.
For the US liquid gallon: 1 gal = 231 cubic inches = 3,785.411784 mL exactly. For the Imperial gallon used in the UK, Canada and elsewhere: 1 gal = 4.54609 L = 4,546.09 mL exactly. So 1 gallon of water (density 1.000 g/mL) weighs about 3,785 g ≈ 8.345 lb (US) or 4,546 g ≈ 10.022 lb (Imperial).
All preset densities are values at approximately 20 °C and standard atmospheric pressure, taken from standard physical-chemistry references. Density varies slightly with temperature — for example, water is densest at 4 °C (1.0000 g/mL) and slightly less dense at 20 °C (0.9982 g/mL). For most practical purposes the difference is negligible, but chemical or industrial calculations may require a temperature-specific density.
Frequently asked questions
1 US liquid gallon = 3,785.41 mL. Water at 20 °C has a density of about 0.9982 g/mL, so 1 US gallon of water ≈ 3,785.41 × 0.9982 ≈ 3,778.6 g ≈ 3.779 kg. Using the exactly 1.000 g/mL approximation gives 3,785.4 g.
Gasoline (petrol) has a density of roughly 0.720–0.775 g/mL; a representative value is about 0.737 g/mL. So 1 US gallon of gasoline ≈ 3,785.41 × 0.737 ≈ 2,790 g ≈ 2.79 kg ≈ 6.15 lb. The exact value varies with blend and temperature.
Because the US liquid gallon (3,785 mL) is smaller than the Imperial gallon (4,546 mL) by about 20%. So for the same substance, 1 Imperial gallon always weighs about 20% more than 1 US gallon. Always check which gallon a source uses — fuel prices and recipe weights can differ significantly.
Also known as
TG we-Calculate Editorial Team. (2026). Gallons to Grams Calculator — Convert by Liquid Density [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/gallons-to-grams-calculator
TG we-Calculate Editorial Team. "Gallons to Grams Calculator — Convert by Liquid Density." TG we-Calculate. 2026. https://we-calculate.com/calculator/gallons-to-grams-calculator.
TG we-Calculate Editorial Team, "Gallons to Grams Calculator — Convert by Liquid Density," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/gallons-to-grams-calculator
@misc{wecalculate_gallons_to_grams_calculator, title = {Gallons to Grams Calculator — Convert by Liquid Density}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/gallons-to-grams-calculator}}, year = {2026}, note = {TG we-Calculate} }
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