What Is a Vehicle’s Fuel Economy?

The terms fuel efficiency and fuel economy are often used interchangeably, but only fuel economy provides a specific number for a vehicle’s fuel consumption. Fuel economy measures how far a vehicle can travel on a certain amount of fuel — in the U.S., that measurement is miles per gallon (mpg) for gas-powered cars.

For example, a vehicle with a fuel economy rating of 30 mpg means it can go 30 miles on a gallon of gas. Fuel efficiency is a general term that refers to how well a certain vehicle uses fuel, so the higher a car’s fuel economy the more fuel-efficient it is.

Vehicles with a lower fuel economy rating burn more fuel to travel the same distance as cars with a better rating, so they tend to cost more to operate and emit more pollution.

The U.S. Environmental Protection Agency (EPA) determines the mpg rating for specific makes and models of cars, based on the car manufacturer’s self-reporting and the EPA’s testing. You can research fuel economy ratings for vehicles dating back to 1984 at fueleconomy.gov, which uses EPA data.

When you buy a new car or certain trucks at a dealership, you can find the vehicle’s estimated mpg on the window sticker where it’s federally mandated to appear.

The EPA provides this information in three categories: city driving, highway driving and combined (an average of city and highway). That’s because the amount of gas used differs by the kind of driving. For example, driving in a city usually requires more stopping and starting than on a highway. Accelerating more often uses more gas and lowers a car’s mpg and fuel efficiency.

The EPA’s mpg figures offer general guidance when determining a vehicle’s fuel efficiency, and the information is useful for comparing vehicles. However, the actual mpg each car obtains depends on many factors, such as whether the car owner does regular maintenance or tends to regularly drive at excessive speeds.

If you’re trying to determine your vehicle’s fuel economy and efficiency, there are several approaches you can take.

Use this formula. Take note of your odometer reading when filling your gas tank. When it’s time to fill your tank, note the new odometer reading and how many gallons of gas it took to fill the tank. Subtract the first odometer reading from the second one to determine how many miles you went between gas fill-ups. Divide that figure by how many gallons of gas it took to fill your car the second time. This will give you the mpg. You may want to do this several times to get an average, because driving may change between fill-ups.

Use an online calculator. NerdWallet’s gas mileage calculator and comparison tool figures your car’s mpg based on your input. You can also compare your car’s annual fuel cost with other vehicles.

Check your car’s dashboard. Most newer vehicles keep track of how efficiently your car is using fuel and will show you a digital mpg display.

An MPGe rating, or miles per gallon equivalent, is used for hybrid and electric cars. It was developed by the EPA to measure and compare an electric vehicle’s energy consumption level to a gas-powered vehicle’s fuel consumption. According to the formula, using 33.7 kWh of power is equivalent to using 1 gallon of gas. So, an electric vehicle that travels 100 miles on 33.7 kWh would have a 100 MPGe rating.

With the average gas price in the U.S. at more than $3 a gallon, operating a gas-powered vehicle can be expensive, especially if you drive a lot. Choosing a more fuel-efficient car can result in significant cost savings over time.