Specific gravity is the ratio of the chemical weight per gallon divided by the weight of water per gallon (8.33 lb per gallon). As an example, if a chemical weighs 10 lb per gallon, the specific gravity of the chemical is 10.0/8.33 = 1.2 SG. (Metric: kilogram/cubic meter or gram/liter) Substances with a specific gravity greater than 1.0 are heavier than water, those with a specific gravity of less than 1.0 are lighter than water. Ace Roto-Mold standard tanks have a specific gravity of 1.7. Our vertical tanks ranging from 20-625 gallons are standard with a specific gravity of 2.0.