How to Keep Gas Mileage Records

Tracking Online or On Paper Shows True Fuel-Economy Numbers


  • Recording Fuel Efficiency

    Recording Fuel Efficiency

    Recording your fuel efficiency almost becomes like a game for some people. The winner is the person who drives farthest on a gallon of gas. | March 18, 2010

Do you know what kind of fuel economy your car gets? You might have a rough idea based on the Environmental Protection Agency (EPA) estimates listed on the car's window sticker. Or maybe you have a sense of the gas mileage from how often you fill up and how much gas the tank holds. But to really know where you stand, you have to keep accurate records. The results might surprise you.

If you regularly start computing your fuel efficiency, you can find ways to save money on gas and know how to budget for the future. You can modify your driving habits and see what kind of improvements that makes in gas mileage. And maybe you'll find this recordkeeping fun.

There are two ways to approach fuel-economy tracking: online and old school.

The online approach is simple. Sign up with a Web site dedicated to mileage tracking. There are several out there including MPGTune.com and Fuelly.com. You enter via your computer or smartphone and all the sites do all the computational work for you. Some sites let you compare your car's performance with other users who drive cars of the same make, year and model as yours.

If you decide to use the paper-and-pen route (which is what we do here at Edmunds with our long-term test cars), there are a few things you'll need to do to get started. The first step is to buy a small notebook and keep it, along with a pen, in the door panel of your car. Create six columns in the notebook and label them in this order: date, odometer, trip, gallons, MPG, notes.

Date: This is the date you buy gas. This will help you budget for gas by showing you how often you fill up the tank.

Odometer: In this column, record the car's odometer reading when you get gas.

Trip: The trip meter is usually in the same area as the odometer. Reset it each time you get a full tank of gas. It will show how far you go between tanks of gas.

Gallons: This is the amount of gas required to refill the tank. You should lock the gas pump handle on and let it shut off automatically. Then, do not top off the tank. Each gas pump will shut off at a slightly different level, but there is no other way to verify that you have a full tank of gas. Later, you will be able to average the miles-per-gallon readings you get to find the lifetime average.

MPG: This is the miles per gallon you got for the previous tank of gas. We will show you how to calculate this later.

Notes: In this column you can make a note about any factors that might have affected the fuel mileage. Perhaps you left the car idling a long time. Maybe you did a lot of stop-and-go driving. Maybe you went into the mountains. This will explain any unusually high or low readings that you get.

After you set up your notebook, get a full tank of gas and drive. When the needle gets to about a quarter tank, fill up again. Now it's time to see what kind of gas mileage you got on this tank of gas. Your mileage from tank to tank will vary. You should look for a pattern before drawing conclusions about your mileage. Also, you will eventually want to average your individual readings to get a "lifetime" average mileage.

Calculating Gas Mileage

This is easy. In fact, if the readings are round numbers, you can do this in your head. For example, if you fill up your tank and it takes 20 gallons of gas and you drive 400 miles, then you divide 400 by 20. That's 20 miles per gallon. However, you often will drive 261.8 miles and buy 12 gallons of gas. In that case, turn to another page of the notebook and do long division. Or use the calculator on your smartphone. Either way, you should come up with 21.82 mpg. Record this figure in the notebook.

After a few months of calculating your fuel efficiency, your MPG column might look like this: 19, 18, 22, 25, 19, 27. You will want to know the average of all these figures, and to get that, add all the numbers in the "trip" column and all the numbers in the "gallons" column. Now divide the total number of miles travelled by the total number of gallons to get the lifetime average.

What It All Means

Now you know that your car isn't getting the 26 mpg listed on the window sticker. The next step is to find ways to improve your mileage. Performing simple maintenance should be your first course of action. Once you get your car serviced, check the mileage again and with any luck, you will see a difference. In some cases the improvement could be dramatic. Also bear in mind that in cars with large engines, small improvements are actually more significant than they appear. For example, an improvement from 12 mpg to 15 mpg is actually a 20 percent improvement.

Your next improvement strategy would be to modify your driving habits. This, too, can produce significant fuel-efficient gains. At Edmunds.com, we see very different gas mileage readings among test drivers who have different driving styles, and in a tightly controlled test editors saw that calm driving produced significantly better fuel economy than did aggressive driving.

Finally, by becoming more aware of the amount of gas you are using, you can make a better choice the next time you go car shopping. Edmunds compiles lists of fuel-efficient cars and trucks. If these don't suit your needs, check the specs for any vehicle on our site and you'll see the EPA estimated fuel economy. The EPA also has lists of top performers.

Tracking your fuel economy gives you insight into your car's performance and your own performance as a mileage-conscious driver. It also gives you a baseline, and an incentive to improve. So get online or get that notebook and get started today.

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