Fill the fuel tank completely
Reset the trip odometer to zero
Drive normally until refueling
Record the distance traveled
Record the amount of fuel used to refill the tank
Divide distance traveled by fuel used
Express the result as miles per gallon, kilometers per liter, or liters per 100 kilometers
Formula: Fuel efficiency = Distance traveled ÷ Fuel used
For liters per 100 kilometers, use: Fuel efficiency = (Fuel used ÷ Distance traveled) × 100