Miles Per Gallon (MPG): Everything You Need to Know

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What does MPG mean?

Miles per gallon, or mpg for short, is the way that we measure a vehicle's fuel consumption in the United States. In the simplest terms, your car's mpg can be determined by taking the number of miles you've driven divided by the gallons used. If you go 100 miles and use 5 gallons of fuel, you're getting 20 miles per gallon. Easy, right?

Of course, knowing a vehicle's mpg is only part of the story. While miles per gallon describes how efficient an internal combustion engine vehicle is, there are other measurements that might be more important to you as a car buyer and we're going to explain them.

Jump to:
How is MPG determined on cars?
What's considered good MPG?
How to calculate miles per gallon?
How do I see my MPG in the car?
What is MPGe?

How is MPG determined on cars?

The Environmental Protection Agency performs a series of test driving routines, also called "cycles" or "schedules," with specific speeds for several driving scenarios. They account for things such as highway driving, city driving, cold temperatures and air-conditioner use. These tests are performed in a laboratory every year on most new vehicle models. After that, the EPA assigns an estimated mpg figure for city, highway and combined driving conditions. These mpg figures appear on the window sticker of nearly every new vehicle, in a designated "Fuel Economy and the Environment" section. This article goes into more detail about the EPA label and the information it contains.

What's considered good MPG?

When most people shop for a car, a big consideration is whether or not it gets good gas mileage. The idea of good gas mileage is relative, based on the type of vehicle being driven. For example, if you are looking at full-size trucks, one that gets 20 mpg on the highway is pretty good, but if you found a small passenger car that gets 20 mpg on the highway, that'd be pretty bad.

The idea of good mpg has also changed as technology has advanced. Good gas mileage 30 years ago is different from good gas mileage today. Even the EPA testing and estimates have changed to be more accurate. In 2008, the EPA updated its methodology to account for faster, more realistic speeds and acceleration, air-conditioner use, and colder outside temperatures. Since all of these factors lower fuel economy, the 2008 changes ended up lowering the mpg estimates for all vehicles. The EPA tweaked its testing formula again for the 2017 model year, which caused some models to lose about 1-2 mpg. If you're wondering about the mpg estimates for a car older than the 2016 model year, take a look at the EPA's mpg comparison tool.

One way to quantify "what's good mpg?" involves comparing it to the national average fuel economy for that vehicle type. The U.S. Department of Energy has a really handy chart that will give you a good idea of where your vehicle stands.

Let's take that hypothetical 20 mpg full-size truck. We said that 20 mpg would be considered good fuel economy for that type of vehicle, and the DOE figures back that up, with a national average of 17.8 mpg for that category. Average passenger cars return 24.4 mpg, while what it calls "ridesourcing" vehicles (think Uber or Lyft) do slightly better at 25.5 mpg. The latter makes sense given the types of vehicles used for that work are largely gas-electric hybrids.

It might seem logical that upgrading from a lower-mpg car to one with a higher estimate will always save you money, but there are diminishing returns when you get past 25 mpg. It is more impactful to go from a 12.5 mpg truck to a 25 mpg sedan than it is to go from a 25 mpg sedan to a 50 mpg hybrid. Intrigued? Take a look at "The Truth About Fuel Consumption" for a different way to calculate how much you spend on fuel.

We also have a Car Cost vs. Gas Mileage Calculator to help you determine if a car with better mpg on paper will actually save you money.

How to calculate miles per gallon

While the government gives fuel economy figures for most vehicles, those numbers are based on a specific test that may or may not describe how your vehicle behaves with your driving style or in your geographic location. This is where the phrase "Your mileage may vary" comes from. For example, if you live in a place with a lot of hills, your average mpg will be lower than the number on your window sticker. If you live somewhere flat with mostly highways, your mpg will likely be better than the government's figures.

If you want to calculate your specific vehicle's average fuel economy for your use case, it's pretty easy to do, but it can take some time. You need to: 

1. Start with a full tank of gas.
2. Reset the trip meter on your car's dashboard or center screen.
3. When it's time to refuel, make a note of how many miles you've driven.
4. Divide the miles driven by the gallons of gas used to fill up the tank. (Check the pump or your receipt.)
5. The figure you get is your mpg for that particular tank.

If you want to see your average mpg over time, you need to keep a record of several tanks of fuel, and then divide by the number of tanks you recorded. So, if you track your mpg for five tanks and those tanks got 25 mpg, 28 mpg, 21 mpg, 19 mpg and 20 mpg, respectively, you would have an average fuel consumption of 22.6 mpg. Several smartphone apps, such as Fuelly, can help with mpg tracking if you don't want to do the math or keep a notebook entry.

How do I see my MPG in the car?

Cars today can display both a real-time calculation of mpg (the readout that moves quickly up and down as you drive) and an estimated average mpg over a period of time (the figure that remains more stable). These are good tools for a quick snapshot of your mpg, but they are not as accurate as calculating it manually per tank. In fact, these fuel economy gauges can often be overly optimistic because automakers often vary in their approach to programming them.

What is MPGe?

When you look at the window sticker of an electric or plug-in hybrid vehicle, you'll see a figure used to describe its efficiency that's called MPGe, which stands for "miles per gallon equivalent." If this seems like a confusing way to measure electric efficiency, don't worry, it is, but it can still be useful when cross-shopping alternative fuel vehicles.

MPGe is calculated based on the "potential energy" of a gallon of gasoline, which is defined as 33.7 kilowatt-hours. To calculate an EV's MPGe, you take the number of miles you've traveled, say 100 miles, and multiply that by 33.7. This gives us 3,337, which we divide by the amount of electric energy used to travel that 100 miles, say 20 kilowatt-hours. This calculation gives us a total of 168.5 MPGe, which we can use to compare with other vehicles to find the most efficient.

The problem with MPGe is that it's only useful for comparison and doesn't translate to the real world because it fails to take into account all the friction and heat losses that vehicles experience during use. So take it with a grain of salt.

With a plug-in hybrid, it is much easier to separate the gas and electric figures rather than try to figure out its MPGe. For example, on a 2024 Toyota RAV4 Prime, the EPA estimates it can travel 42 miles on its electric battery. Once the battery is discharged, the engine takes over, and it gets an EPA-estimated 38 mpg in mixed driving.

On an electric vehicle, it is easier (and more accurate) to look at the kilowatt-hours (kWh) per 100 miles figure on the EPA label. With this figure, it is the opposite of MPG, in that a lower number is better. Here's an extreme example to illustrate the point. Let's compare the 2024 Hyundai Ioniq 6 Standard Range RWD, with its EPA estimate of 25 kWh/100 miles, to the 2025 GMC Sierra EV, which gets 52 kWh/100 miles.

How is fuel efficiency described outside the U.S.?

While we here in the U.S. use mpg to describe fuel economy, the rest of the world has adopted the metric system, which means that most places use another type of unit, liters per 100 kilometers. In the most basic terms, that means that instead of describing how far a vehicle will go on a set unit of fuel, this approach describes how much fuel a vehicle uses to go a set distance. In the end, both measurements do the same thing. One key difference: With mpg, you want to see a larger number, but with L/100km, you want to see a smaller number if you're looking for a more efficient vehicle.