One US gallon of water weighs approximately 8.34 pounds (about 3.785 kilograms) at room temperature, which is around 70°F (21°C)

. The exact weight can vary slightly depending on temperature because water density changes with temperature-colder water is denser and heavier, while warmer water is less dense and lighter

. To summarize:

• Weight of 1 US gallon of water ≈ 8.34 pounds (3.785 kg) at room temperature
• Weight range varies roughly between 8.29 and 8.35 pounds depending on temperature
• Weight changes because water expands or contracts with temperature, affecting density

This value assumes standard Earth gravity and sea-level atmospheric pressure. Different conditions like altitude or gravity (on other planets) would affect the weight

. In contrast, an imperial gallon (used in the UK) weighs about 10.02 pounds (4.546 kg) because it is a larger volume