How To
By
eHow Cars Editor
Difficulty: Moderately Easy
Step1
Fill the gas tank completely. Write down the mileage on the odometer reading before leaving the gas station.
Step2
Create a log to record the mileage and number of gallons every time you fill up. Keep it in an easy to access place, such as the glove compartment.
Step3
Refill the tank to the top, when it's time to refuel, using the same grade of gasoline as was used during the initial fill. Log the number of gallons required to fill the tank and the odometer reading.
Step4
Subtract the previous odometer reading from the second to calculate the distance driven.
Step5
Calculate the miles per gallon by dividing the number of miles driven by the total gallons of gas it took to fill the tank the second time.