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Friday Fuel Economy: mpg Math

By John Rockhold


Tags: gas mileage, gas prices, mpg math, mpg tips,

The first step to improving your car or truck's fuel economy is to know how many miles per gallon it really gets. Calculating mpg is easy, even if you hate math. Plus, monitoring your fuel economy and becoming more aware of what influences it is one of the simplest ways you can make a difference for the environment and your wallet.

Here's how to do the math. It's easier than you might think.  

1. Fill up your tank.

2. Reset your trip meter to zero.

3. Get gas when you need it.

4. Record the number of gallons it took to fill your tank and the number of miles on your trip meter. You could write these numbers down in a small notebook, or perhaps an easier place is the gas receipt. Usually these already include the number of gallons you bought.

5. Reset the trip meter before you restart the car (so you can check your fuel economy again next time).

6. Divide the trip miles by the gallons of gas. Congratulations, with just simple division, you've calculated your car's mpg. For example: 298.7 miles ÷ 8.475 gallons = 35 mpg.

7. Whether you use a small notebook or a simple spreadsheet on your computer, track your fuel economy over time. It can be fun and rewarding, especially as you learn habits to improve your mpg. It will also give you a better understanding of how your car is performing and can signal potential maintenance needs before they become big problems. If a few calculations reveal dramatic declines from the norm and you don't have an obvious explanation, consider calling your mechanic. Another idea is to record basic notes on fuel economy influences such as speed, tire pressure, driving conditions, extra loads and use of air conditioning. This will help you better understand what driving habits most influence mpg. Tracking fuel economy will also give you a richer understanding of just how much money you spend on gas and how much oil driving requires.

Now you know how to do the math. Make it a personal challenge to improve your fuel economy. Tell us about calculating your mpg, and improving it, in the comments section below.


John Rockhold is a green car enthusiast and Contributing Editor for MOTHER EARTH NEWS. Find him on .

mike mackaman
11/23/2008 11:48:19 AM

I love the challenge your articles have laid down to all of us. I recently purchased a '90 Civic Si for $2200 to become my daily driver. I parked my '04 GMC Sierra extended cab truck that got 17 mpg. My "new" civic gets 30 mpg around town, and has gotten 34.3 mpg on the highway. I could probably get much better by changing my style, but the bottom line is that I use 25 gallons less gas every month. We use it as much as possible on weekends, and other trips around town. Thanks again for the challenge to our conventional way of thinking.