For liquids such as fuels, specific gravity is the weight of that liquid divided by the weight of water. Fuels are lighter than water, so the specific gravity of fuels is less than 1. Let’s look at an example. Turbo Blue 110 weighs 6.19 pounds per gallon and water weighs 8.33 pounds per gallon. Applying some math: 6.19 / 8.33 = 0.743. So Turbo Blue 110’s specific gravity is 0.743. If Fuel A has a lower specific gravity than Fuel B, Fuel A is said to be “lighter” than Fuel B. Literally, a gallon of Fuel A would weigh less than a gallon of Fuel B. Knowing a fuel’s specific gravity is important when it comes to fuel systems. Changes in specific gravity can affect how both carburetors and fuel injection systems meter fuel. When changing fuels, it is usually easier to switch to a fuel with a similar specific gravity.