Water's weight matters more often than you might think: a full tub or hot tub on a floor, a water tank in a truck bed, rain barrels on a deck, or a heavy pot of hot water. A gallon of cool fresh water weighs 8.34 lb per US gallon, and the calculator adjusts for temperature, salt and ice.
How to use this calculator
- Enter the amount and pick the unit.
- Choose the water: fresh at a temperature, seawater or ice.
- Read the weight, and the weight per gallon for that kind of water.
Worked examples
A five-gallon jug
Amount: 5 · Unit: US gallons · Water: Fresh water, cool (60 °F)
- Weight
- 41.7 lb
- Per gallon
- 8.34 lb per gallon
- US gallons
- 5
- Liters
- 18.93 L
- Cubic feet
- 0.668 cu ft
A full bathtub
Amount: 40 · Unit: US gallons · Water: Warm bath water (100 °F)
- Weight
- 331.5 lb
- Per gallon
- 8.29 lb per gallon
- US gallons
- 40
- Liters
- 151 L
- Cubic feet
- 5.35 cu ft
A water heater tank
Amount: 50 · Unit: US gallons · Water: Hot water (120 °F)
- Weight
- 412.6 lb
- Per gallon
- 8.25 lb per gallon
- US gallons
- 50
- Liters
- 189 L
- Cubic feet
- 6.68 cu ft
A thousand liters of seawater
Amount: 1,000 · Unit: Liters · Water: Seawater
- Weight
- 2,261 lb
- Per gallon
- 8.56 lb per gallon
- US gallons
- 264
- Liters
- 1,000 L
- Cubic feet
- 35.32 cu ft
- Short tons
- 1.13 tons
A cubic foot of ice
Amount: 1 · Unit: Cubic feet · Water: Ice
- Weight
- 57.2 lb
- Per gallon
- 7.65 lb per gallon
- US gallons
- 7.48
- Liters
- 28.31 L
- Cubic feet
- 1 cu ft
How much a gallon of water weighs
The USGS gives a gallon of water as 8.34 lb per US gallon. Its density table shows how that shifts with temperature: a cubic foot weighs 62.424 lb per cubic foot near freezing, where water is heaviest, 62.3 lb per cubic foot at room temperature, 61.386 lb per cubic foot as very hot water and 59.843 lb per cubic foot at the boil. A cubic foot holds 7.48 US gallons, which turns those into pounds per gallon.
Seawater and ice
Salt makes seawater heavier: NOAA uses 64 lb per cubic foot. Ice is lighter than the water it came from, with a density of about 0.917 grams per cubic centimeter, because water grows by about 9 percent in volume as it freezes. That is why ice floats, and why a full container can crack when it freezes.
Common questions
How much does a gallon of water weigh?
About 8.34 lb per US gallon for cool fresh water. Hot water weighs slightly less and seawater more.
How much does a liter of water weigh?
Close to a kilogram for cool fresh water. The calculator gives the exact figure for the temperature you pick.
Does hot water weigh more than cold water?
No, slightly less. Water is heaviest near freezing and gets lighter as it warms: a cubic foot weighs 62.424 lb per cubic foot near freezing and 59.843 lb per cubic foot at the boil.
How much does a cubic foot of water weigh?
About 62.366 lb per cubic foot for cool fresh water, and 64 lb per cubic foot for seawater.