How much does a gallon of water weigh in pounds, stones and kilos
How much does a gallon of water weigh depends on where it is and the temperature.
Temperature
Let me explain, the temperature is simple, if the water is heated it causes the molecules to expand – to move apart. So a container that has a volume of 1 gallon will weigh less than one that has cold water in it, as the molecules are closer together and so can fit more water into the container.
As an experiment weigh a pint, or a liter, of water at home that is cold and then boil the water – now reweigh the same heated pint, or liter of water, and see the weight has gone down.
Location
The ‘where’ is more complex. Basically the altitude (pressure) also effects the weight as does gravity etc. But far too complex for our needs in this summary.
More importantly the where in terms of US or UK location makes a big difference. You see a liter is the same in both but a gallon is not.
Metric System (Liters or Litres)
The metric system using liters (litres in UK and Europe) is fairly straightforward. At a temperature of 4 degrees Celsius (39.2ºF), exposed to standard atmospheric pressure of 101.325 kPa, 1cm³ of water is 1ml, and weighs 1 gram. 1 Liter of water (1000ml) weighs 1kg (1000g).
Simple to remember that 1 liter of water weighs 1 kilogram. (at 4ºC).
Gallons – the confusion begins!
A gallon in the US and UK are not the same measure!
In the US 1 gallon of water is 128 fluid ounces, or 3.785 liters. In the UK it is 160 fluid ounces, or 4.546 litres.
It is best that we stick to comparing liters because just as the size of a gallon differs so does the size of a fluid ounce.
(1 Imperial fluid ounce = 0.9607603 US fluid ounces.)
The point to note is that a UK gallon is a little over 20% bigger than a US gallon.
For example, a 50 Gallon Tank in UK would hold 60 US Gallons of water.
Water Weight
The following two tables identify how much water weighs at a room temperature of 70°F / 21°C and 80°F / 26.7°C. Most aquariums at home will be within this range.
| Weight of water in pounds, stones and kilos for US gallons | |||
| Gallons of water | Pounds | Stones | Kilos |
| 1 gallon | 8.33 lb | 0.60 | 3.78 kg |
| 2 gallons | 16.66 lb | 1.19 | 7.56 kg |
| 3 gallons | 24.99 lb | 1.79 | 11.33 kg |
| 4 gallons | 33.32 lb | 2.38 | 15.11 kg |
| 5 gallons | 41.64 lb | 2.97 | 18.89 kg |
| 6 gallons | 49.97 lb | 3.57 | 22.67 kg |
| 7 gallons | 58.3 lb | 4.16 | 26.45 kg |
| 8 gallons | 66.63 lb | 4.76 | 30.22 kg |
| 9 gallons | 74.96 lb | 5.35 | 34 kg |
| 10 gallons | 83.29 lb | 5.95 | 37.78 kg |
| 15 gallons | 124.933 lb | 8.92 | 56.67 kg |
| 20 gallons | 166.578 lb | 11.83 | 75.56 kg |
| 29 gallons | 241.538 lb | 17.25 | 109.56 kg |
| 30 gallons | 249.866 lb | 17.85 | 113.34 kg |
| 40 gallons | 333.155 lb | 23.80 | 151.12 kg |
| 50 gallons | 416.444 lb | 29.75 | 188.90 kg |
| 60 gallons | 499.733 lb | 35.70 | 226.67 kg |
| 100 gallons | 832.888 lb | 59.49 | 377.79 kg |
| 120 gallons | 999.466 lb | 71.39 | 453.35 kg |
| 150 gallons | 1249.332 lb | 89.24 | 566.69 kg |
| At room temperature (70°F / 21°C) | |||
| Weight of water in pounds, stones and kilos for US gallons | |||
| Gallons of water | Pounds | Stones | Kilos |
| 1 gallon | 8.318 lb | 0.59 | 3.773 kg |
| 2 gallons | 16.636 lb | 1.19 | 7.546 kg |
| 3 gallons | 24.953 lb | 1.78 | 11.319 kg |
| 4 gallons | 33.271 lb | 2.38 | 15.092 kg |
| 5 gallons | 41.589 lb | 2.97 | 18.864 kg |
| 6 gallons | 49.907 lb | 3.56 | 22.637 kg |
| 7 gallons | 58.224 lb | 4.16 | 26.41 kg |
| 8 gallons | 66.542 lb | 4.75 | 30.183 kg |
| 9 gallons | 74.86 lb | 5.35 | 33.956 kg |
| 10 gallons | 83.178 lb | 5.94 | 37.729 kg |
| 15 gallons | 124.767 lb | 8.91 | 56.593 kg |
| 20 gallons | 166.356 lb | 11.88 | 75.458 kg |
| 29 gallons | 241.216 lb | 17.23 | 109.414 kg |
| 30 gallons | 249.533 lb | 17.82 | 113.186 kg |
| 40 gallons | 332.711 lb | 23.77 | 150.915 kg |
| 50 gallons | 415.889 lb | 29.71 | 188.644 kg |
| 60 gallons | 499.067 lb | 35.65 | 226.373 kg |
| 100 gallons | 831.778 lb | 59.41 | 377.288 kg |
| 120 gallons | 998.134 lb | 71.30 | 452.746 kg |
| 150 gallons | 1247.667 lb | 89.12 | 565.932 kg |
| At room temperature (80°F / 26.7°C) | |||
Aquarium Dimensions and Typical Tank Sizes
If you want to calculate the volume of your tank and need a quick calculator to see how many gallons or liters it holds go to our ‘Aquarium Calculator‘ page.
Or check out our article that tells you the typical dimensions for various standard tank sizes HERE.
