How to Calculate Fuel Cost

Calculating Your Vehicle's MPG

A customer pumps gas into her car at a gas station in San Jose, Calif.
A customer pumps gas into her car at a gas station in San Jose, Calif.
AP Photo/Marcio Jose Sanchez

In commercials and advertisements for cars we often see MPG, or miles per gallon, featured prominently. Most of us know that a higher MPG is more desirable because it equates to less visits at the gas station. But what does that number really mean?

Essentially, MPG tells you how many miles your car can travel on a single gallon of gas. If, for example, your car gets 34 miles per gallon, then traveling 34 miles should consume exactly one gallon of gas.


We usually see two different figures -- city MPG and highway MPG. These figures are determined by the federal Environmental Protection Agency, which rates the fuel economies of new cars after rigorous testing on a dynamometer. City MPG refers to driving with occasional stopping and braking, simulating the conditions you're likely to run into while driving on city streets. Highway MPG is based on more continuous acceleration, which usually yields a higher figure because it's a more efficient use of the engine.

However, these figures aren't necessarily the same as what you would get in everyday life. Everyone drives differently. These tests don't take into account how fast a driver drives, when they choose to shift gears (if they use a manual transmission), or road conditions unique to your area. In other words, your results may vary.

Here's how to figure out your own personal MPG: First, fill your gas tank and then reset the trip odometer. Drive until your car's gas tank is nearly empty, or close enough to it that you need more gas immediately. Look at how many gallons of gas it took to fill up the tank completely. Now take the reading on the odometer -- the number of miles you've driven since your last fill up -- and divide it by the number of gallons used.

In other words, if you have an empty tank and put 10 gallons of gas in it, then see that you traveled 350 miles, you're getting 35 miles per gallon. Over time, this will give you an accurate measurement of how efficiently you drive your car in real-world situations.