Fuel tank capacity is the amount of fuel that fits into an automobile's fuel tank. The owner's manual of a vehicle normally includes the fuel tank capacity.
The exact amount of gas the fuel tank holds may vary from the fuel tank capacity listed in the owner's manual. Slight variations in the design and manufacturing process can change the actual amount by up to 3 percent, according to the Kansas Department of Agriculture.
Knowing the fuel tank capacity helps consumers estimate gas consumption and fuel efficiency of the vehicle. If the owner knows the tank holds approximately 12 gallons of gas, he can track how many miles he drives on the tank to determine the vehicle's miles per gallon.