The owner's manual for a vehicle typically provides a good estimate of its fuel tank capacity. However, manufacturers warn that actual fuel tank capacity may differ from intended capacity. These variations are a result of normal fluctuations in the manufacturing process and other factors.
Not included in a manufacturer's estimate of fuel tank capacity are the vapor head space and the filler pipe. These are areas where the fuel goes if a driver "tops off" the tank by delivering more fuel after the pump automatically shuts off.
Consumers frequently assume their vehicle's gas gauge level accurately reflects how much fuel is in the tank, but that isn't necessarily the case. If the vehicle is not on level ground, the gas gauge's reading may be incorrect. There are also other variables that can cause false gas gauge readings.