Liquid Weight Calculator
Gallons, liters, cups or cubic feet of water, milk, gasoline, diesel, propane — with cited densities.
Everything is computed locally in your browser — nothing is uploaded.
How to use
- 1
Choose a liquid
Water, milk, gasoline, diesel, liquid propane and more.
- 2
Enter a volume
US gallons, imperial gallons, liters, milliliters, cups, fl oz, m³ or ft³.
- 3
Read the weight
See kg and lb instantly, computed from the liquid’s cited density.
How it works & limits
Weight = volume × density. Volume definitions are exact (NIST Handbook 44 Appendix C: 1 US gal = 231 in³ = 3.785411784 L; 1 imperial gal = 4.54609 L). Densities come from cited sources: water density at 21 °C (0.99802 g/cm³) is from the USGS Water Science School; fuel densities are from the US Department of Energy.
Water is temperature-sensitive: the calculator offers temperature choices only where a sourced density table exists for that temperature. If a temperature isn’t listed, we don’t show it.
Example: 1 US gallon of water at 21 °C = 3.785411784 L × 0.99802 kg/L = 3.78 kg (8.33 lb).
FAQ
How much does a gallon of water weigh?
About 8.33 lb (3.78 kg) at 21 °C — the USGS publishes exactly 8.33 pounds/gallon, and the density table gives 0.99802 g/cm³ at 21 °C (70 °F).
Is a US gallon the same as an imperial gallon?
No. 1 US liquid gallon = 3.785 L; 1 imperial gallon = 4.546 L — about 20% more, so an imperial gallon of water weighs about 10.02 lb (4.54 kg).
Why does the same liquid give different weights on different sites?
Density varies with temperature and grade (summer vs winter gasoline, for example). This calculator always states the temperature condition next to the density it uses.