Fill the fuel tank completely
Reset the trip odometer or record the starting odometer reading
Drive normally until you need to refuel
Fill the tank completely again
Record the miles driven from the trip odometer or by subtracting the starting odometer from the ending odometer
Record the gallons of fuel added to refill the tank
Divide miles driven by gallons used
MPG = Miles Driven ÷ Gallons Used
Example: 300 miles ÷ 10 gallons = 30 MPG