Key Takeaways
- MPG measures how many miles a gasoline vehicle travels on one gallon of fuel.
- MPGe lets you compare electric and gas vehicles using the same energy-per-mile scale.
- EPA ratings come from standardized lab tests; real-world results vary with driving habits and conditions.
- A higher MPG or MPGe number always means lower fuel or energy cost per mile.
- Window sticker estimates include annual fuel cost projections based on average US driving and fuel prices.
Fuel economy rating
A fuel economy rating tells you how far a vehicle travels on a given amount of fuel or energy. For gasoline vehicles, it is expressed in miles per gallon (MPG). For electric and plug-in hybrid vehicles, the EPA also uses miles per gallon equivalent (MPGe), which converts electricity consumption into a gasoline-equivalent number so different powertrains can be compared on the same scale.
The EPA derives MPGe from the energy content of one gallon of gasoline (33.7 kilowatt-hours), then calculates how many miles an EV travels on that same amount of electrical energy.
How MPG is calculated
The Environmental Protection Agency (EPA) tests every new vehicle sold in the US and assigns city, highway, and combined MPG figures. The combined rating blends 55% city and 45% highway driving, which is what appears most prominently on the window sticker.
Testing happens on a dynamometer, a device that simulates road conditions indoors. EPA engineers run vehicles through standardized driving cycles that replicate stop-and-go traffic, moderate highway speeds, high-speed highway travel, cold-start conditions, and air conditioning use. The results are then adjusted downward using correction factors because real-world driving consistently produces lower numbers than the pure lab output.
The window sticker also shows an estimated annual fuel cost based on a fixed assumption of 15,000 miles per year and a national average fuel price. That figure is a planning tool, not a guarantee. If you drive more miles or pay more for gas than the national average, your actual cost will be higher.
Read the window sticker carefully
The Monroney sticker on every new vehicle shows city, highway, and combined ratings separately, plus a range indicating how much real-world results can vary. Check the 'actual results will vary' range rather than focusing only on the combined number, because it shows you the realistic floor for efficiency in less favorable conditions.
What MPGe means for electric and hybrid vehicles
When a vehicle runs on electricity, the gallon-of-gas framework no longer applies directly. The EPA bridges that gap with MPGe. One gallon of gasoline contains approximately 33.7 kilowatt-hours (kWh) of energy. The EPA measures how many miles an electric vehicle travels on 33.7 kWh and reports that distance as its MPGe.
A vehicle rated at 100 MPGe, for example, travels 100 miles on the same energy content as one gallon of gasoline. Because electricity is generally cheaper per unit of energy than gasoline in most US markets, a high MPGe vehicle often costs less to run per mile than its MPG equivalent would suggest, though electricity prices vary considerably by state and time of use.
Plug-in hybrid vehicles (PHEVs) carry two ratings: an MPGe figure for electric-only operation and a standard MPG figure for when the gasoline engine takes over. The EPA window sticker shows both, along with a combined estimate that reflects typical usage splitting between the two modes.
For a broader look at how these powertrain differences affect your wallet over time, see our comparison of lifetime fuel and energy costs across gas, electric, and hybrid vehicles.
33.7 kWh
Energy equivalent of one gallon of gasoline
The EPA uses this figure as the basis for converting EV electricity consumption into MPGe.
55% / 45%
City vs. highway weighting in combined MPG
The EPA's combined rating blends city and highway results using a 55-to-45 split to reflect typical US driving patterns.
15,000
Annual miles assumed on the window sticker
The EPA bases its annual fuel cost estimate on 15,000 miles per year, which is close to the US national average for passenger vehicles.
Why your real-world numbers will differ
Several factors consistently pull actual efficiency below the EPA estimate. Speed has a large effect: aerodynamic drag increases significantly above 60 mph, so highway driving at 75 or 80 mph burns more fuel than the highway test cycle assumes. Cold weather reduces both gasoline engine efficiency and, more sharply, the range of battery-electric vehicles because the battery itself loses capacity in low temperatures.
Payload matters too. Carrying extra passengers, towing a trailer, or loading a truck bed raises fuel consumption in proportion to the added weight. Air conditioning is another consistent drain, particularly in city driving where the engine runs at lower, less efficient speeds.
On the other side, some drivers beat the EPA estimate. Smooth, consistent driving at moderate speeds, coasting to decelerate before stops, and pre-conditioning an EV while it is still plugged in during winter are all techniques that help close the gap.
If you are weighing an EV against a gas vehicle and want a full picture of what those efficiency differences mean for total ownership costs, our EV vs. gas vehicle cost and practicality breakdown covers the key financial trade-offs in detail.
Using ratings to compare vehicles and budget fuel costs
The combined MPG or MPGe figure is the most practical number for everyday comparison because most people split their driving between city and highway. When two vehicles are close in price, the one with a meaningfully higher combined rating will cost less to operate over time, and that difference compounds over years of ownership.
To estimate your own annual fuel cost for a gasoline vehicle, divide your expected annual mileage by the vehicle's combined MPG, then multiply by your local average fuel price. For an EV, divide your annual mileage by the vehicle's efficiency in miles per kWh (found on the window sticker alongside MPGe), then multiply by your local electricity rate in dollars per kWh.
The EPA's fueleconomy.gov website lets you run these calculations with your own inputs and compare multiple vehicles side by side. It also publishes historical data so you can see how specific models have rated over multiple model years, which helps when evaluating a used vehicle purchase.
One number the sticker does not capture is how efficiency changes as a vehicle ages. A well-maintained engine or battery holds its efficiency better over time, which means factoring maintenance habits into any long-term fuel cost projection gives a more accurate picture than the sticker estimate alone.