How to Calculate the Cost of Gas


Before you embark on a car trip, it’s a good idea to calculate how much you need to spend on fuel. The cost of gas you need will depend on many factors, including the fuel efficiency of your car, your local gas prices and the type of roads you are primarily driving on. If you have to start and stop a lot, you will use more gas and therefore have to spend a bit more. If you drive regularly, you can also calculate how much you need to spend on gas monthly or yearly.

Things You'll Need

  • Calculator
  • Internet access
  • Determine the number of miles you will be traveling. To do this quickly, enter your origin and destination addresses in an online map site, such as Google Maps or Yahoo! Maps (see Resources). Click the “Get Directions” link, enter the addresses and then click the “Get Directions” button. Choose the route you want, and take note of the total mileage. If you are making a round trip, multiply this number by 2. For example, if you making a round trip that is 250 miles one way, the total mileage would be 500, because 250 x 2 = 500.

  • Determine the fuel efficiency of your car. This tells how many miles the car goes per gallon of gas that is used. The rate will change depending on how much you stop and start. That’s why fuel efficiency is separated into city and highway rates. Go to the U.S. Department of Energy’s Fuel Economy site (see Resources) to find the gas mileage for your car model. Under “Find and Compare Cars,” click “Compare Side-by-Side.” Select your year, make and model to find your car’s average MPG value.

  • Divide the total miles you found in Step 1 by the MPG value of your car. This will give you the total number of gas gallons you need to purchase. Continuing the example from Step 1, if the gas mileage is 25 MPG, then 500 / 25 = 20.

  • Multiply the number of gallons by the average gas price (per gallon) in your region. The result is what you need to spend on gas for your trip. Continuing the example from Step 3, if the average price is $3 per gallon, then 20 x $3 = $60.

Tips & Warnings

  • If you’re going on a long trip, you may just want to estimate with the national average. You can find gas price averages online or in a local newspaper (see Resources).

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  • Photo Credit old gas pump image by Brett Bouwer from
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