Water weight calculator.
One US gallon of water weighs 8.33 lb (3.779 kg) at 20 °C (68 °F). Five gallons weigh 41.7 lb. One liter weighs 0.998 kg. Above 4 °C, warmer water weighs slightly less per gallon.
Enter a volume and the water temperature. The calculator uses the CIPM-recommended density of pure water.
How much does water weigh? Quick answers
Weights of pure water at 20 °C (68 °F). Containers are not included.
| Volume | Weight (lb) | Weight (kg) |
|---|---|---|
| 1 US cup | 0.52 lb | 0.236 kg |
| 1 liter | 2.20 lb | 0.998 kg |
| 2 liters | 4.40 lb | 1.996 kg |
| 1 US gallon | 8.33 lb | 3.779 kg |
| 1 UK gallon | 10.00 lb | 4.538 kg |
| 2.5 US gallons | 20.83 lb | 9.447 kg |
| 5 US gallons (water jug) | 41.65 lb | 18.893 kg |
| 10 US gallons | 83.30 lb | 37.786 kg |
| 1 cubic foot | 62.32 lb | 28.266 kg |
| 30 US gallons | 249.91 lb | 113.359 kg |
| 55 US gallons (drum) | 458.17 lb | 207.824 kg |
| 100 US gallons | 833.04 lb | 377.862 kg |
| 1 cubic meter | 2,200.67 lb | 998.207 kg |
| 300 US gallons | 2,499.13 lb | 1,133.587 kg |
| 1,000 US gallons | 8,330.44 lb | 3,778.624 kg |
Water density by temperature
The table shows how the weight of one US gallon changes with temperature. From 4 °C to 40 °C, the density falls by 0.78 %.
| Temperature | Density (kg/m³) | kg per liter | lb per US gallon |
|---|---|---|---|
| 0 °C (32 °F) | 999.84 | 0.99984 | 8.344 |
| 3.98 °C (39.2 °F) | 999.97 | 0.99997 | 8.345 |
| 5 °C (41 °F) | 999.97 | 0.99997 | 8.345 |
| 10 °C (50 °F) | 999.70 | 0.99970 | 8.343 |
| 15 °C (59 °F) | 999.10 | 0.99910 | 8.338 |
| 20 °C (68 °F) | 998.21 | 0.99821 | 8.330 |
| 25 °C (77 °F) | 997.05 | 0.99705 | 8.321 |
| 30 °C (86 °F) | 995.65 | 0.99565 | 8.309 |
| 35 °C (95 °F) | 994.03 | 0.99403 | 8.296 |
| 40 °C (104 °F) | 992.22 | 0.99222 | 8.280 |
How the calculation works
- Convert the volume to liters. One US gallon is exactly 3.785411784 L.
- Find the density of water at the given temperature with the CIPM formula.
- Multiply the volume by the density. The result is the mass in kilograms.
- Divide the kilograms by 0.45359237 to get pounds.
ρ(t) = a5 × [1 − (t + a1)² (t + a2) / (a3 (t + a4))] kg/m³ a1 = −3.983035 °C a2 = 301.797 °C a3 = 522528.9 °C² a4 = 69.34881 °C a5 = 999.974950 kg/m³ (t in °C, 0 to 40)
Common questions
How much does a gallon of water weigh?
One US gallon of pure water weighs 8.33 lb (3.779 kg) at 20 °C (68 °F). At 4 °C (39 °F) it weighs 8.35 lb. The often quoted 8.34 lb is the value near 15.6 °C (60 °F): 8.337 lb.
How much do 5 gallons of water weigh?
Five US gallons of water weigh 41.7 lb (18.9 kg) at 20 °C. A full 5-gallon jug weighs more, because the jug has its own weight.
Does a liter of water weigh 1 kg?
Almost. One liter of pure water is 1.0000 kg at 4 °C and 0.9982 kg at 20 °C. So 1 kg per liter is accurate to about 0.2 % at room temperature.
Does hot water weigh less than cold water?
Yes, above 4 °C and for the same volume. Water is densest at about 4 °C (3.98 °C). Above that, it expands as it gets warmer. A US gallon weighs 8.345 lb at 4 °C and 8.280 lb at 40 °C. Between 0 °C and 4 °C, water gets slightly denser as it warms.
How much does a UK gallon of water weigh?
One UK (imperial) gallon is 4.54609 L. It holds 10.00 lb (4.538 kg) of water at 20 °C. That is about 20 % more than a US gallon.
Do tap water and sea water weigh the same as pure water?
Not exactly. Dissolved minerals and salt add mass. Sea water is denser than pure water. Tap water is very close to pure water. This calculator is for pure water.
Sources
- Water density: M. Tanaka et al., "Recommended table for the density of water between 0 °C and 40 °C based on recent experimental reports", Metrologia 38 (2001) 301–309. This is the formula recommended by the CIPM for metrology (pure, air-free water at 101.325 kPa).
- US gallon, quart, cup, fluid ounce and pound: NIST Handbook 44, Appendix C (exact definitions).
- UK gallon (4.54609 L): Weights and Measures Act 1985, Schedule 1.