How to Easily Calculate and Track Your Car’s Gas Mileage

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diesel pump

Fuel efficiency is one of the hottest statistics that car manufacturers tout in their advertisements today. No one wants to spend more money than necessary by being forced to fill up the gas tank several times a week.

Regardless of how you think your current automobile does on gas, however, it’s always worth it to keep track of your actual gas mileage. By doing a simple calculation every time you fill up the tank, you can monitor your fuel efficiency and easily notice when abrupt changes might signal a problem with your engine.

How to Calculate Gas Mileage

Gas Meter

Figuring out your car’s gas mileage is actually extremely easy–especially once you get into the habit of calculating it each time you stop for fuel. The first step is to get a full tank of gas and write down the current total mileage of your car. Label this number “Mileage A,” and then store your notepad somewhere in your car where you won’t lose it.

Next, you can drive as you normally would until the tank needs refilling. This time, when you stop to get gas, you’ll want to write down the total number of miles that you drove since last filling up (call this number “Mileage B”). By subtracting Mileage A from Mileage B, you can find out how far you drove between fill-ups (you can label this number “Total Mileage”). You should also write down the exact amount of gas you purchased at the pump, which will usually be a total number of gallons that is accurate to three decimal places (label this number “Gallons”).

To find out how many miles your car was able to drive per gallon of gas, divide Total Mileage by Gallons. Depending on the fuel efficiency of your car, you may get a number anywhere from 10 MPG (which is pretty abysmal) up to 70 MPG (which would be considered great). Record this calculation on a separate page with the date. Now you can repeat the process the next time you get gas, except this time you will need to calculate the difference between Mileage B and a new “Mileage C” in order to find out your Total Mileage.

Keep Track of Gas Mileage


While manually calculating your gas mileage isn’t that difficult, it can be much less time consuming to let a computer do the calculations for you. A number of smartphone apps exist for all major mobile platforms that will track your fuel efficiency. Just enter your total mileage and the number of gallons purchased each time you fill the tank, and apps like Gas Cubby, Road Trip, or Mileage Keeper will tell you your MPG. These apps will also track your car’s progress over time so that you can compare all your tanks and come up with an average MPG.

As you repeat this process for a while, you will likely start to notice some trends developing. For instance, if you drive in the city a lot and stay away from highways, your gas mileage is likely to be much worse than if you take a long road trip and constantly drive 65 MPH. If you start to notice any inexplicable changes in your fuel efficiency, however, it’s a good idea to bring your car in to your mechanic and get your engine checked for any problems. Keeping track of fuel efficiency is a quick and easy way to monitor the impact your car has on the environment and on your wallet.