The density of water is 1kg per litre.
a gallon is 5 litres so it weighs 5kg
A gallon of regular water weighs about 8 pounds
1 US gallon= 3.785 l
Density of water= 1 kg/l
density= mass/volume
1 kg/l = m/ 3.785 l
m = 3.785 kg
- Had this been an imperial gallon than m= 4.546 kg
Weight= mg= 3.785 kg*9.81 m/s
2=37.1 kg*m/s2=37.1 N=8.34 pounds