A gallon of water weighs approximately 8.34 pounds (about 3.78 kilograms) at room temperature or around 62°F (17°C)

. This value corresponds to the US liquid gallon, which is defined as 3.785 liters. The weight can vary slightly depending on temperature, pressure, and gravitational conditions, since colder water is denser and weighs a bit more, while warmer water weighs slightly less

. In summary:

• US liquid gallon of water ≈ 8.34 lbs (3.78 kg) at typical room temperature.
• Weight varies slightly with temperature and altitude.
• UK (imperial) gallon weighs about 10.02 lbs (4.55 kg) due to a larger volume definition

Thus, for everyday purposes, you can remember that one US gallon of water weighs about 8.34 pounds.