Be Your Own Fuel Economy Calculator

We're not here to talk about how improving gas mileage or to complain about the difference between EPA mileage estimates and what you really get. We may get to that some other time, but for now you'll have to look elsewhere.

This is a plain old arithmetic class that I'd like to think will help people calculate their own gas mileage (AKA "fuel economy" or "MPG"). It doesn't make sense to say that it costs $50 to fill your car's tank, because 1) the tank capacity isn't the same from vehicle to vehicle and 2) the distance since the last fill-up varies, too. This is - like I said - a tutorial:



Calculate Gas Mileage in Miles per Gallon.

Doing this is almost ridiculously easy in the era of trip odometers*. Here's how you do it:

1:  Fill the gas tank, letting the pump run until it automatically shuts off. Don't top off the tank, because it adds to air pollution and wastes some of the gas you just bought.
2:  Zero out your trip odometer. You'll find instructions in the owner's manual if you need them.
3:  Drive until you need to fill the tank again. Repeat step 1, and get a receipt showing the number of gallons you've used.
4:  Record or memorize the distance from the trip odometer.

OK, now you have two numbers: The distance you've gone and the number of gallons you burned doing it. To calculate fuel economy in MPG, divide that first number by the second.

MPG = distance traveled ÷ gallons consumed

The number is reported as "miles per gallon" (MPG) in the US.

Example
1) It took 21.7 gallons to fill your Escalade. You've driven 365.5 miles since your last fill-up. Your gas mileage is calculated using the formula

MPG = 365.5 ÷ 21.7
Your fuel economy = 16.8 MPG (miles per gallon)

2) It took 11.2 gallons to fill your Prius Sedan and it's been 501.1 miles since you last filled up. Your gas mileage can be calculated using the formula

MPG = 501.1 ÷ 11.2
Your fuel economy is 44.7 MPG (miles per gallon).

Since results vary with driving conditions, you should calculate your mileage over several fill-ups to get a good feeling for the fuel economy of your ride. We all tend to get lower mileage during our daily commutes than on long highway drives, which is why the EPA reports estimated City and Highway numbers.

What does this all mean? Well, the cost of filling the Escalade is about twice that of filling the Prius, but the hybrid's mileage is between two and three times that of the Caddy.

There: you don't have an excuse to express gas mileage in "dollars per fill-up" any more!


* If you don't have a trip odometer, don't despair: just jot your odometer mileage down on the receipt every time you fill up and do the subtraction. Feel free to use a calculator if you must.