Gas Mileage: Calculate Your MPG

Automotive, Home & Family
on October 15, 2011

When in the market to buy a car, you might consider a certain brand for a variety of reasons. These features include seating, horsepower, overall reliability, amenities and gas mileage. Typically, the manufacturer will state the mileage of the car in print, and this is broken into “city” driving and “highway” driving. These are broad designations, as most of us will engage in what is generally referred to as “mixed” driving. In order to calculate the actual mileage, drivers need to understand their driving patterns and do some specific calculations.

Doing the math. Overall, the miles per gallon (mpg) represents how many miles are driven on a single gallon of gas. The U.S. Department of Energy website describes two methods for calculating your vehicle’s mpg. Here’s one method:

Step 1: Fill the vehicle’s gas tank completely and write down the odometer reading (mileage).Example: The last time the tank was filled the odometer reading was 32,645.1 miles.

Step 2: When it’s time to refuel, fill the tank completely, and again write down the number of gallons it took to fill up, and the new odometer reading. Example: The next time the tank was filled, the odometer reading was 33,001.3 and it took 13.5 gallons.

Step 3: Calculate the distance driven by subtracting the previous odometer reading from the new one. Example: 33,001.3 minus 32,645.1 equals 356.2 miles.

Step 4: Divide the number of miles driven by the number of gallons it took to fill the tank. This is the vehicle’s mpg for that driving period. Example: 356.2 miles divided by 13.5 gallons equals 26.4 mpg.

Impacting factors. In a given gas tank, the mileage can vary from one gallon to the next, depending on the style of driving. The only way for the mpg to remain almost consistent is to maintain the same general speed over a period of time, which can sometimes happen on road trips. However, most people drive differently as they go about their day. Some drivers travel on freeways, while others spend a lot of time on city streets or sitting at stoplights. In addition, mpg can be impacted by weather and how much you use the air conditioner.

Maintenance and repairs. As cars age, mpg also can be impacted by wear-and-tear issues. It’s wise to monitor your vehicle and perform regular maintenance, such as oil changes, filter changes and tune-ups. Some drivers will diligently check their mileage at every fill-up, while others check periodically to see if anything has changed drastically. The savvy driver will pay attention to mpg in order to detect issues before they turn into big problems.