Since the density of water is 1 g/cm^3, therefore sand weighs 2.2 /1 = 2.2 times as much as water for a given volume. ie... 1 gallon of water weighs 8.35 lbs so 1 gallon of sand weighs 8.35 x 2.2 = 18.4 lbs so the sand weighs more...Source(s):Dr W · 8 years ago.he gallon of water would be lighter I believe because its a question of the densities of the two. Sand would be more dense than water, around 1600kg/m^3 and water is 1000 or 1026 for salt water.