GraceM-CC

The weight of water in ounces does not equal the number of fluid ounces. Water weighs about 8.3 lbs per gallon depending on the exact temperature, elevation, and other factors. A pound is 16 ounces, so a gallon of water weighs (has a mass of) about 133 ounces. A gallon has 128 fluid ounces, so a fl oz of water weighs about 1.04 ounces. 12 fl oz of water therefore weighs about 12.5 ounces. A fl oz of wax is lighter than a fl oz of water, because wax is less dense than water (wax floats in water).