conversions
How Much Does a Gallon of Water Weigh
Last updated: May 31, 2026
Written by Blake Boege
A gallon-of-water-weight page calculates water mass based on volume. At room temperature, a US liquid gallon weighs approximately 8.34 pounds (3.78 kilograms). An Imperial (UK) gallon weighs exactly 10.00 pounds (4.54 kilograms). Water weight varies slightly depending on its temperature and density.
Find out the exact weight of water in pounds or kilograms. Use our instant weight-to-volume converter and explore how temperature alters liquid density.
Quick Answer
Determine the exact weight of water in pounds or kilograms for US and Imperial liquid gallons.
How Much Does a Gallon of Water Weigh?
A US gallon of water weighs approximately 8.34 pounds (3.78 kg).
An Imperial gallon (UK) of water weighs exactly 10.00 pounds (4.54 kg).
Liquid System
Note: Based on water density at room temperature (approximately 62°F / 17°C).
US Customary Water Weight Table
| Volume (US Gallons) | Weight in Pounds (lbs) | Weight in Kilograms (kg) |
|---|---|---|
| 1/2 Gallon | 4.17 lbs | 1.89 kg |
| 1 Gallon | 8.34 lbs | 3.78 kg |
| 2 Gallons | 16.69 lbs | 7.57 kg |
| 5 Gallons | 41.73 lbs | 18.92 kg |
| 10 Gallons | 83.45 lbs | 37.85 kg |
Examples
1 Gallon of Water (US)
8.34 lbs / 3.78 kg
1 Gallon of Water (Imperial)
10.00 lbs / 4.54 kg
5 Gallons of Water (US)
41.70 lbs / 18.91 kg
How it works
The weight of water depends on volume and density. At room temperature (62°F / 17°C), water has a density of approximately 0.999 g/mL:
US Gallon Weight
1 US Gallon ≈ 8.34 pounds (3.78 kg)
Imperial Gallon Weight
1 Imperial Gallon = 10.00 pounds (4.54 kg)
How Temperature and Pressure Affect Water Weight
Water is unique because its density peaks at 39.2°F (4°C). As it cools below this temperature toward freezing, or as it heats up, its molecules spread out, meaning it takes up more space for the same amount of mass.
For everyday home, pool, and construction calculations, using the standard factor of 8.34 lbs per gallon is highly accurate and widely accepted.
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Frequently asked questions
The Imperial measurement system was designed with water as its foundation. By historical definition, one Imperial gallon was defined as the volume occupied by exactly 10 pounds of distilled water weighed in air under specific temperature and atmospheric pressure conditions.
No. Water expands as it heats up, making it less dense. A US gallon of near-boiling water (200°F) weighs about 8.04 pounds, whereas a gallon of ice-cold water (39°F, where water is most dense) weighs 8.345 pounds.
Milk has a higher density than water, weighing about 8.6 pounds per gallon. Gasoline is much less dense, weighing about 6.0 to 6.3 pounds per gallon.
Five US gallons of water weighs approximately 41.7 pounds (18.9 kg), excluding the weight of the plastic bucket or container (which typically adds 1-2 pounds).
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