How to Read an EV Efficiency Rating on the Window Sticker
Two figures on the window sticker describe how efficient an electric car is: MPGe and kWh per 100 miles. MPGe is the big number, but kWh per 100 miles is the one you can turn directly into a charging cost, so it deserves more of your attention when you read an EV efficiency rating on the window sticker.
Both come from the same standardized EPA testing, and both appear on the fuel economy label that new cars in the U.S. carry. They just express the result in different units.
What MPGe means
MPGe stands for miles per gallon equivalent. The EPA treats 33.7 kWh of electricity as containing the same energy as one gallon of gasoline, then reports how far the car travels on that amount of energy. It was designed so shoppers could compare an electric car with a gas car on a familiar scale.
The trouble is that you never buy electricity by the gallon. A high MPGe tells you the car uses energy efficiently, but it does not tell you what a mile costs, because that depends on your electricity rate rather than gas prices. MPGe also follows the same pattern as MPG: the jumps look larger at the high end than they really are in energy terms.
kWh per 100 miles avoids both problems. Lower is better, and it scales in a straight line. Multiply it by your cost per kWh and you have the cost of driving 100 miles, before charging losses. For the same driving on the same electricity plan, the car with the lower figure costs less to run.
The rest of the EV efficiency rating on the window sticker
The EPA’s own guide to the electric vehicle label walks through each section. The ones worth checking:
| Label item | What it tells you | What to keep in mind |
|---|---|---|
| Combined, city and highway MPGe | Efficiency on the EPA test cycles | Useful for comparing models, not predicting your own use |
| kWh per 100 miles | Energy used per distance | The figure to multiply by your electricity rate |
| Driving range | Estimated miles on a full charge | Drops in cold weather and at sustained highway speed |
| Charge time | Time to charge on a 240V circuit | Depends on your equipment and the car’s onboard charger |
| Annual fuel cost | Estimated yearly energy cost | Based on EPA’s assumed mileage and electricity price, not yours |
| Greenhouse gas and smog ratings | Tailpipe emissions score | Does not include emissions from generating electricity or making the battery |
How far to trust the numbers
The label is a lab result, applied the same way to every car. That makes it excellent for comparing two models side by side and less reliable as a forecast of your own driving. Speed, temperature, load and terrain all change consumption. We go into that gap in real-world EV range vs the EPA estimate, and winter adds its own penalty, covered in our guide to cold-weather EV range.
The annual fuel cost line deserves a second look, too. It assumes a national average electricity price, which may be well above or below what your utility charges. Redo that sum with your own rate before treating it as a savings figure.
When you compare two EVs on a lot, look at kWh per 100 miles first. It is the one number on the sticker that converts straight into dollars.
