A gallon of water weighs approximately 8.34 pounds (about 3.78 kilograms) at room temperature (around 70°F or 21°C)

. This weight can vary slightly depending on temperature, as colder water is denser and heavier, while warmer water is less dense and lighter

. The standard US gallon is defined as 3.785 liters, and since 1 liter of water weighs about 1 kilogram, this translates to roughly 3.78 kg per gallon