There are many sites that allow you to check the mileage for the make and model of your car. However, your own driving styles and habits may vary significantly from the ideal conditions of the test drives, so it's more accurate to calculate your own mileage if you are serious about gas economy and saving money. You may be surprised at how much (or how little) mileage you get, compared to the official estimates.
Wait to begin calculating your mileage until you need to fill up your tank, and don't fill up your tank until it is as close to empty as possible. It will make this exercise easier for you if you start with an empty tank, so it's best to wait for your gas light to come on before you fill up.
Record the number of gallons that you put into your tank to fill it up. Your tank will probably never be completely full or empty, but filling it up right after the gas light comes on should minimize those differences.
While you are still at the pump, record the number of miles that are on your odometer. If you have a trip odometer, you can set the trip odometer to zero and just let it run, which will make your calculations easier later on.
Drive as you normally would until your gas light comes on again.
Record the number of miles on your odometer as soon as your gas light comes on. If you zeroed out your trip odometer at the beginning of this period, then this is the number of miles that you will use for your calculations. If you are using your regular odometer, subtract the number of miles of your first reading from the number at this reading. For example, if your starting mileage was 40,401 miles and your ending miles were 40,616, then your total mileage was 215 miles.
Divide the number of miles that you drove by the number of gallons that you used to fill up your tank. In this example, if you filled up your tank with 14.5 gallons of gas, you would divide 215 by 14.5 to get 14.8 miles per gallon.
