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How Much Does a Gallon of Water Weigh? The Definitive Answer
Quick Answer
A US gallon of water weighs exactly 8.34 lbs (3.785 kg) at room temperature. An Imperial gallon (UK, Canada older usage) weighs 10.02 lbs (4.546 kg) because it is 20% larger. One US fluid ounce of water weighs almost exactly 1 oz by weight.
Try the AI Digital ScaleUS gallon of water
8.34 lbs
3.785 kg, 128 fl oz
Imperial (UK) gallon
10.02 lbs
4.546 kg, 20% larger
1 liter of water
~2.2 lbs
1 kg exactly at 4°C
Water Weight by Volume
Water density is so consistent that volume-to-weight conversions are essentially exact for everyday use.
| Volume | Weight (lbs) | Weight (kg/g) |
|---|---|---|
| 1 fl oz | 0.065 lb | 29.6g |
| 1 cup (8 fl oz) | 0.52 lb | 236g |
| 1 pint (16 fl oz) | 1.04 lb | 473g |
| 1 quart (32 fl oz) | 2.09 lb | 946g |
| 1/2 gallon | 4.17 lb | 1.89 kg |
| 1 US gallon | 8.34 lb | 3.785 kg |
| 1 Imperial gallon | 10.02 lb | 4.546 kg |
| 5 gallons (bucket) | ~42 lb | ~19 kg |
| 1 liter | 2.2 lb | 1.000 kg (at 4°C) |
How Temperature Affects Weight
Water is densest at 4°C (39°F), where 1 liter = exactly 1.000 kg. At room temp (20°C / 68°F), 1 liter = 0.998 kg. At boiling (100°C / 212°F), 1 liter = 0.958 kg, about 4% lighter due to expansion. Negligible for everyday use, only matters for lab work.
Why It Matters
Camping water adds 8.34 lbs per gallon to your pack. A 10-gallon aquarium holds 83 lbs of water (plus tank and gravel). A water heater holds 30-50 gallons (250-417 lbs) and must be drained before moving. A 400-gallon hot tub weighs 3,300+ lbs of water alone, requiring reinforced floor support.
Water as a Reference Weight
A gallon jug is a great reference. Six gallon jugs = ~50 lbs (the standard checked-bag limit). A 5-gallon bucket = ~42 lbs. Two cases of bottled water = ~50 lbs. Use these as instant comparisons for unknown objects.
Frequently Asked Questions
How much does a gallon of water weigh in pounds?+
A US gallon of water weighs exactly 8.34 lbs (3.785 kg) at room temperature. An Imperial gallon (UK, Canada older usage) weighs 10.02 lbs (4.546 kg).
How much does 5 gallons of water weigh?+
5 US gallons of water weighs 41.7 lbs (18.93 kg). A 5-gallon water cooler jug plus the bottle itself weighs about 43 lbs total.
Does water weigh the same as ice?+
Per volume, no. Ice is less dense than liquid water (about 920 kg/m^3 vs 1000 kg/m^3), which is why ice floats. Per mass, the same number of grams of water and ice weigh the same.
How much does 1 liter of water weigh?+
One liter of water weighs exactly 1 kg (2.2 lbs) at 4°C. At room temperature it is about 998g. The metric kilogram was originally defined as the mass of 1 liter of water.
How much does a 16 oz bottle of water weigh?+
A 16.9 fl oz (500 ml) bottle of water weighs about 1.1 lbs (500g) of water plus the bottle (10-15g). So total weight is about 510-515g per bottle.
Why is the Imperial gallon heavier than the US gallon?+
The Imperial gallon (used historically in the UK and Canada) is 20% larger than the US gallon: 4.546 liters vs 3.785 liters. So an Imperial gallon of water weighs 10.02 lbs vs 8.34 lbs for a US gallon.
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