With the rising cost of gas and the proliferation of new automobile technologies, it’s important to understand just how much that gas-powered vehicle is costing you. Thankfully it’s not that hard to figure out, and involves a few simple calculations.

Your actual gas efficiency, measured in miles per gallon (mpg) or kilometers per liter (kpl), may vary from the estimates given to you by your manufacturer. That’s because the condition of your vehicle and your style of driving, among other factors, will influence just how much mileage you’ll get after you fill up. For more information on how to get the most from each tank of gas, read Eartheasy’s guide to Fuel-Efficient Driving.

Here’s how to calculate the gas mileage for your car.

Calculating Your Car's Miles per Gallon (MPG)

Fill Up and Record

  1. Fill up your gas tank all the way.
  2. If your car has a trip odometer, reset it, or record the master odometer mileage.
  3. Drive your car as you normally would, and let your gas tank deplete to at least a half of a tank of gas.
  4. Get to the gas station and fill your tank again.
  5. Record the amount of gas it took to refill the tank.
  6. Record the elapsed trip miles or new odometer mileage.


  1. Get the miles traveled from the trip odometer, or subtract the original odometer reading from the new one.
  2. Divide the miles traveled by the amount of gallons it took to refill the tank. The result will be your car’s average miles per gallon yield for that driving period.

Here’s the formula: miles driven gallons used = mpg

You can perform the same steps to calculate kilometres per litre.
kilometers driven liters used = kpl

Here’s an example: 312 miles driven ÷ 16 gallons fueled = 19.5mpg

Repeat this procedure every time you refill your tank can help you monitor and improve your gas mileage. Improving your fuel efficiency is possible!

But what about cost? How much does it cost you to drive your car? Finding that out adds another step.

How to Calculate Your Rate of Gas

You’ve already calculated how many miles (or kilometers) per gallon (or liter) you can drive in your car. Using that number, you can find out how much it costs you to drive your car per distance measured. Here’s how.

Take the average price that you pay at the pumps per gallon and divide that by the number you found when you calculated mpg for your car. Here’s the formula:

price per gallon miles per gallon = price per mile

Again, you can use a variation of the same equation to calculate price per kilometer:

price per liter kilometers per liter = price per kilometer

Once you’ve found out how much it costs you to travel per unit of measure, you can apply that price to the distance of whatever trip you’re planning. This will tell you how much a given trip will cost in your particular car.

Knowing these amounts can help you improve both your fuel efficiency and your savings every time you drive.

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