How to Calculate Fuel Economy

A fuel-efficient car can save money at the gas pump.

Fuel economy shows how well your car uses gas to generate power. In the United States, fuel economy is typically measured in miles per gallon. The higher your fuel economy, the more efficiently your car is running.

Things You'll Need

• Calculator

Instructions

1. Write down the odometer reading when you fill up your car with gas, and call this M1. Be sure to fill the tank completely.

2. Drive your car until you need to fill up again.

3. Write down the odometer reading (call this M2) when you fill up with gas the second time. Also note the number of gallons (call this G) you put in your car. Fill the gas tank completely.

4. Plug the values from Steps 1 and 3 into the following equation: (M2 - M1) / G. If your initial odometer reading is 13,400, your final reading is 13,670 and you used 13 gallons of gas, the expression would be (13,670 - 13,400) / 13. That equals about 20.8 miles per gallon.

Tips & Warnings

• Your fuel economy will vary over time. If you do mostly highway driving one tank and city driving the next, you will get two different fuel economy ratings.

• If you notice a sudden drop in fuel mileage, something may be wrong. A faulty oxygen sensor, for example, can drop fuel economy by as much as 40 percent.

References

• Fuel Economy.gov: Calculating Your MPG
• Fuel Economy.gov: Keeping Your Car In Shape