How to use the water weight calculator
Pick fresh water or sea water, type the temperature, and type how much water you have. The page gives the weight in pounds, kilograms and tons at once. Pick weight from the I know the box and it works backward to the volume. The Tank, pool or pond tab works out the volume from the size of the container, and the Other liquids tab handles anything with a specific gravity you can type. The temperature starts at 68 °F (20 °C), and the picture shows the water poured onto a scale and counted as one-gallon jugs.
The formula
pounds = US gallons × 3.785411784 × density (kg per liter) ÷ 0.45359237
A US gallon is exactly 231 cubic inches, which is exactly 3.785411784 liters, and a pound is exactly 0.45359237 kilogram. A milliliter is exactly a cubic centimeter, so a density in grams per cubic centimeter is also kilograms per liter. At its heaviest, near 39 °F (4 °C), water is 1.000 kg per liter, which makes a US gallon of water 8.3454 pounds. The common rounded figures are 8.34 pounds per gallon, 62.4 pounds per cubic foot and 1 kilogram per liter.
A worked example
A standard 55-gallon drum is full of water at 68 °F. The volume is 55 × 3.785411784 = 208.198 liters. The density of water at 68 °F is about 0.99823 kg per liter. The mass is 208.198 × 0.99823 = 207.83 kg, and 207.83 ÷ 0.45359237 = 458.18 pounds. The rounded rule of 8.34 pounds per gallon gives 55 × 8.34 = 458.7 pounds, about a tenth of a percent high. The drum weighs about 458 pounds of water, or 0.229 US ton, before you count the drum.
Does the temperature matter?
A little. Water is densest at about 39 °F and gets lighter as it warms, so a gallon of hot water weighs less than a gallon of cold. For most jobs the difference is smaller than the error in measuring the tank.
| Temperature | Pounds per US gallon | Pounds per cubic foot |
|---|---|---|
| 40 °F (4.4 °C) | 8.345 | 62.43 |
| 68 °F (20 °C) | 8.331 | 62.32 |
| 100 °F (37.8 °C) | 8.288 | 62.00 |
| 140 °F (60 °C) | 8.207 | 61.39 |
| 180 °F (82.2 °C) | 8.100 | 60.59 |
| 212 °F (100 °C) | 8.000 | 59.85 |
Sea water, ice, milk, oil and fuel
Salt makes water heavier. Sea water is usually quoted at about 1.025 kg per liter, which is about 8.55 pounds per gallon or 64 pounds per cubic foot. The published figures run from about 1.020 to 1.030, so treat the 1.025 as typical. Ice has the same mass as the water it came from, but it takes up about 9 percent more room, so it floats with most of itself below the surface. A gallon of milk is printed at 8.6 pounds, a little heavier than water. Olive oil is lighter: its legal specific gravity range of 0.910 to 0.916 is about 7.6 pounds per gallon. Fuels are lighter still. The US Department of Energy's fuel properties table prints gasoline at 6.0 to 6.5 pounds per gallon and diesel at about 7.1, both at 60 °F. The page uses 6.25 for gasoline, the middle of its range, and 7.079 for diesel, the value the table prints, and shows the range. An older edition gives diesel as 6.7 to 7.4. The weight changes with the blend, the season and the temperature: check your supplier's sheet. This page is about weight only; gasoline is flammable, so follow your local rules for storing and moving fuel. For anything else, type its specific gravity on the Other liquids tab.
The US gallon is not the imperial gallon. The imperial gallon is 4.54609 liters and holds about 10 pounds of water at room temperature. Pick imperial gallons in the unit list if your numbers come from a UK or Canadian label.
Where the numbers come from
The density of water at each temperature is the table from the USGS Water Science School, which gives the density in grams per cubic centimeter from 32 °F to 212 °F. The page reads between its rows in a straight line, which adds far less error than measuring the tank does. The US gallon is legally 231 cubic inches, or 3.785411784 liters, and the imperial gallon is 4.54609 liters. The sea water figure is a typical value from encyclopedia and handbook sources, not a table value. The 8.6 pounds for milk is from a dairy extension service, and the olive oil range is from the Canadian Food and Drug Regulations. The gasoline and diesel figures are from the Department of Energy's Properties of Fuels table, checked against refinery safety data sheets. If your label gives a different number, type yours.
What people use it for
- Stock tanks, rain barrels, fish tanks and ponds: how much weight is going on a trailer, a stand or the ground.
- Pools and hot tubs: how many tons of water a pool holds, and how many pounds sit on each square foot of its footprint.
- Hauling water: a spray tank, a water tote or a load for a truck bed.
- Checking a delivery sold by the gallon, the liter or the cubic yard.
Common mistakes
- Weighing only the water. The drum, tank, liner and stand add weight. Add them yourself.
- Mixing up the gallons. A US gallon is 3.785 liters and an imperial gallon is 4.546 liters, about a fifth bigger.
- Mixing up the tons. A US ton is 2,000 pounds and a metric tonne is 1,000 kilograms, about 2,205 pounds. The page names which one it shows.
- Using 8.34 for very hot water. At 180 °F a gallon is 8.10 pounds.
Questions
How much does a gallon of water weigh?
About 8.33 pounds for a US gallon at room temperature, 8.345 pounds at its heaviest, and the rounded 8.34 is used everywhere. An imperial gallon holds about 10 pounds.
Does hot water weigh less?
Yes, slightly. A US gallon is 8.345 pounds at 40 °F, 8.33 at 68 °F and 8.00 at 212 °F. The difference is about 4 percent between ice-cold and boiling.
Is a gallon of milk heavier than a gallon of water?
Yes. A gallon of milk is printed at 8.6 pounds, against about 8.33 for water at room temperature.
How much does a cubic foot of water weigh?
About 62.3 pounds at room temperature, 62.43 at its heaviest, and 62.4 as the rounded figure. A cubic yard is about 1,683 pounds, and a cubic meter is about 1,000 kilograms (998 at 68 °F), about 2,200 pounds.
Is gasoline heavier than diesel?
No. Diesel is heavier: about 7.1 pounds a gallon against 6.0 to 6.5 for gasoline, at 60 °F. Both are lighter than water.
Can I use metric?
Yes. Press Metric to type liters, cubic meters and degrees Celsius. The answer leads with kilograms and still shows pounds. The page opens in the system your browser's region uses and remembers your choice.
Can I share my result?
Yes. Share makes a link with a picture for Facebook, a link you can copy, and a short video for TikTok made on your device. The link keeps only the volume, the temperature and whether it is sea water, for 90 days.