How to Calculate Average Miles Per Gallon

Written by karen nehama
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How to Calculate Average Miles Per Gallon
Find out your fuel usage per gallon. (gas pump image by jedphoto from

Knowing the average miles per gallon your vehicle is getting informs you whether the car is meeting the manufacturer's estimated miles per gallon. New car invoices not only detail the cost of the vehicle; they include the estimated miles per gallon that particular vehicle should get when driving in the city and on the highway. Calculate the average miles per gallon on your car to see if your vehicle meets the mileage benchmark. Keep in mind that driving habits, vehicle maintenance and type of fuel used can affect vehicle performance and gas usage.

Skill level:

Things you need

  • Vehicle owner's manual
  • Calculator

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  1. 1

    Read the vehicle's owner's manual to find out what the vehicle's gas tank capacity is. Look up the information on the Internet or speak to a dealership mechanic if you can't determine the gas tank capacity any other way.

  2. 2

    Fill the gas tank on the vehicle to the maximum allowed. Look at the odometer, and write down the current reading.

    How to Calculate Average Miles Per Gallon
    Write down the odometer reading. (Speedometer image by Sirena Designs from
  3. 3

    Drive the car until it is nearly out of gas. Once the vehicle "low on fuel" indicator light comes on, drive just a bit further because most cars still have a gallon or two in the tank after the light goes on.

  4. 4

    Look at the odometer when the gas level is nearly depleted. Record the odometer reading.

  5. 5

    Calculate the odometer difference by taking the final odometer reading and subtracting the original odometer amount. This is how many miles you drove on one tank of gas.

    How to Calculate Average Miles Per Gallon
    Do the calculations. (calculator image by L. Shat from
  6. 6

    Divide how many miles you drove on one tank of gas by the vehicle's gas tank capacity. The resulting figure is how many miles per gallon your vehicle gets.

  7. 7

    Narrow your research further by performing the exercise two or three more times. Divide the total number of all gallons used by the total number of miles driven. The results may be close to your first findings, but a bit more accurate.

Tips and warnings

  • Don't actually run out of gas during your research or you may endanger yourself or wind up stranded.

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