How to Calculate Average Miles Per Gallon

Find out your fuel usage per gallon.

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.

Things You'll Need

• Vehicle owner's manual
• Calculator

Instructions

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. 

   Write down the odometer reading.

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

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

5. 

   Do the calculations.

   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.

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. 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 & Warnings

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

References

• Math: Miles per Gallon
• Fuel Economy: Your Mileage Will Still Vary