The average capacity of a vehicle's gas tank is typically listed on the owner's manual of that specific make and model. However, in most cases, the listed number is an estimate and tends to vary from the actual capacity of the fuel tank.
Alternatively, the fuel capacity of a vehicle can be established by completely emptying the tank, then observing how much gas is required to completely refill it. The fuel system architecture of car depends on the type of car, nozzle model, region and the type of fuel used by the car (diesel or gasoline). Fuel tanks are either molded using high-density polyethylene plastic or welded from stamp sheets of aluminum or steel.