How Much Does a Gallon of Water Weigh?

A US gallon of water weighs about 8.34 pounds (roughly 3.78 kilograms) at room temperature. A UK imperial gallon, which is larger, weighs about 10.02 pounds (roughly 4.55 kilograms).

Quick reference:

• 1 US gallon ≈ 8.34 lb ≈ 3.78 kg
• 1 imperial gallon ≈ 10.02 lb ≈ 4.55 kg
• 1 liter of water ≈ 1 kg (2.2 lb)

Water weight changes slightly with temperature because water expands as it warms. It is densest at about 4°C (39°F), where it weighs the most, and becomes slightly lighter as it heats up. For everyday purposes, though, 8.34 pounds per US gallon is the standard figure to remember.