How Much Does a Gallon of Water Weigh? (lbs/kg)

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)

In summary, multiple gallons of water weigh the amounts listed below:

• 1 gallon of water weighs 8.3454 lbs (3.7854 kg). But REMEMBER the important caveat about temperature above!
• 2 gallons of water weighs 16.69 lbs (7.57 kg)
• 3 gallons of water weighs 25.04 lbs (11.36 kg)
• 4 gallons of water weighs 33.38 lbs (15.14 kg)
• 5 gallons of water weighs 41.73 lbs (18.93 kg)
• 6 gallons of water weighs 50.07 lbs (22.71 kg)
• 7 gallons of water weighs 58.42 lbs (26.50 kg)
• 8 gallons of water weighs 66.76 lbs (30.28 kg)
• 9 gallons of water weighs 75.11 lbs (34.07 kg)
• 10 gallons of water weighs 83.45 lbs (37.85 kg)
• 11 gallons of water weighs 91.80 lbs (41.64 kg)
• 12 gallons of water weighs 100.14 lbs (45.42 kg)
• 13 gallons of water weighs 108.49 lbs (49.21 kg)
• 14 gallons of water weighs 116.84 lbs (53.00 kg)
• 15 gallons of water weighs 125.18 lbs (56.78 kg)
• 16 gallons of water weighs 133.53 lbs (60.57 kg)
• 17 gallons of water weighs 141.87 lbs (64.35 kg)
• 18 gallons of water weighs 150.22 lbs (68.14 kg)
• 19 gallons of water weighs 158.56 lbs (71.92 kg)
• 20 gallons of water weighs 166.91 lbs (75.71 kg)
• 25 gallons of water weighs 208.64 lbs (94.64 kg)
• 30 gallons of water weighs 250.36 lbs (113.56 kg)
• 35 gallons of water weighs 292.09 lbs (132.49 kg)
• 40 gallons of water weighs 333.82 lbs (151.42 kg)
• 45 gallons of water weighs 375.54 lbs (170.34 kg)
• 50 gallons of water weighs 417.27 lbs (189.27 kg)
• 55 gallons of water weighs 459.00 lbs (208.20 kg)
• 60 gallons of water weighs 500.72 lbs (227.12 kg)
• 65 gallons of water weighs 542.45 lbs (246.05 kg)
• 70 gallons of water weighs 584.18 lbs (264.98 kg)
• 75 gallons of water weighs 625.91 lbs (283.91 kg)
• 80 gallons of water weighs 667.63 lbs (302.83 kg)
• 85 gallons of water weighs 709.36 lbs (321.76 kg)
• 90 gallons of water weighs 751.09 lbs (340.69 kg)
• 95 gallons of water weighs 792.81 lbs (359.61 kg)
• 100 gallons of water weighs 834.54 lbs (378.54 kg)
• 110 gallons of water weighs 917.99 lbs (416.40 kg)
• 120 gallons of water weighs 1001.45 lbs (454.25 kg)
• 130 gallons of water weighs 1084.90 lbs (492.10 kg)
• 140 gallons of water weighs 1168.36 lbs (529.96 kg)
• 150 gallons of water weighs 1251.81 lbs (567.81 kg)
• 160 gallons of water weighs 1335.26 lbs (605.67 kg)
• 170 gallons of water weighs 1418.72 lbs (643.52 kg)
• 180 gallons of water weighs 1502.17 lbs (681.37 kg)
• 190 gallons of water weighs 1585.63 lbs (719.23 kg)
• 200 gallons of water weighs 1669.08 lbs (757.08 kg)
• 250 gallons of water weighs 2086.35 lbs (946.35 kg)
• 300 gallons of water weighs 2503.62 lbs (1135.62 kg)
• 350 gallons of water weighs 2920.89 lbs (1324.89 kg)
• 400 gallons of water weighs 3338.16 lbs (1514.16 kg)
• 450 gallons of water weighs 3755.43 lbs (1703.43 kg)
• 500 gallons of water weighs 4172.70 lbs (1892.70 kg)
• 1000 gallons of water weighs 8345.40 lbs (3785.41 kg)
• 2000 gallons of water weighs 16690.80 lbs (7570.82 kg)
• 3000 gallons of water weighs 25036.20 lbs (11356.23 kg)
• 4000 gallons of water weighs 33381.60 lbs (15141.64 kg)
• 5000 gallons of water weighs 41727.00 lbs (18927.05 kg)
• 6000 gallons of water weighs 50072.40 lbs (22712.46 kg)
• 7000 gallons of water weighs 58417.80 lbs (26497.87 kg)
• 8000 gallons of water weighs 66763.20 lbs (30283.28 kg)
• 9000 gallons of water weighs 75108.60 lbs (34068.69 kg)
• 10000 gallons of water weighs 83454.00 lbs (37854.10 kg)

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.