There's a simpler, far superior way to calculate EV energy efficiency.
Check the window sticker on any electric vehicle and you'll see a bizarre metric called MPGe (miles per gallon - equivalent). It was first created by the US Environmental Protection Agency back in 2010 as an easy way for consumers to compare the efficiency of an EV to a gas-powered car. A Hyundai Ioniq 5, for example, is rated at 114 MPGe combined. So compared to a Hyundai Santa Fe with a four-cylinder engine, which is rated at only 26 mpg combined, the Ioniq 5 offers superior efficiency.
This seems self-explanatory enough, but we think MPGe is not a great metric for measuring EV efficiency. It does a poor job of comparing running costs versus an ICE vehicle, makes it difficult to calculate range, and is overall very complicated to calculate. In fact, we feel there is a much simpler stat that should be on the window sticker for every EV sold in America: miles per kilowatt hour (mi/kWh).
If you're at all familiar with electric cars, you know they all come with a battery containing a certain number of kilowatt hours. The aforementioned Ioniq 5 has a 77.4 kWh pack, while the GMC Hummer EV Pickup has a giant 212.7 kWh battery. An EV's battery size is similar to an ICE vehicle's gas tank because it measures how much fuel (in this case, electricity) can be stored. So in order to better compare ICE cars and EVs, we recommend the simple mi/kWh calculation. Some EVs display this number in the gauge cluster, just as an ICE vehicle would show mpg. It lets the driver know how efficient they are being with their electricity in real-time or over a specific distance.
By looking at the mi/kWh number, it's dead simple to figure out how far an EV will go on a charge based on your driving. For example, we observed 3.6 mi/kWh in the Ioniq 5 during a week of testing. Just multiply that number by 77.4 kWh (the usable battery capacity), and the resulting range is 278.64 miles. The EPA rates the dual-motor Ioniq 5 at 266 miles, so our calculation is perfectly believable if the car is slightly more efficient in real-world driving.
Mi/kWh is perfectly easy to comprehend, but it's even more simple when contrasted with MPGe. To calculate MPGe, the EPA uses a formula that compares how much electricity is roughly equivalent to a gallon of gasoline. It would require around 33.7 kWh to generate the same amount of heat as burning a gallon of gasoline, so MPGe is essentially measuring how far an EV can go per 33.7 kWh. That means the Ioniq goes roughly 114 miles per 33.7 kWh, while a less efficient EV like the Hummer only goes 47 miles.
The EPA also publishes another number, kWh/100 miles. This measures how many kWh it takes for an EV to travel 100 miles. In the case of the Hyundai, it's rated at 30 kWh/100 mi. Doesn't this seem far more confusing than our preferred measurement? We can't comprehend how any of this matters to a car buyer looking at a window sticker.
Mpg is a simple and easy way for car owners to calculate how much fuel their car uses. To really dumb it down, if a car gets 30 mpg, that means it can travel 30 miles on one gallon of gas. Stick 10 gallons in the tank, the car should go around 300 miles. Simple. MPGe, despite being intended to allow a comparison to standard mpg, is a far less useful stat. 114 MPGe, doesn't easily let a driver calculate range, which is the most important stat in an EV.
There's also the core crux of why we use mpg in combustion vehicles. The answer is this: because you are seeing how many miles you can drive per unit of fuel. You pay per gallon, so you want to see how far you can travel per gallon. Likewise, when you charge an EV at a public charging station, you pay per kWh, and you are told how many kWhs you've topped up with. The basic premise is the same - how far can you go per unit you purchase.
If the EPA decided to put mi/kWh on the window sticker, even if it was just an average number, we believe this would be a more helpful stat to determine how efficient an EV is with each kWh put into the battery.
While we'd love to see 'mi/kWh' included on the window sticker, it doesn't need to replace MPGe fully. Automakers still rely on MPGe numbers to pull up their fleet's average fuel economy. For example, an F-150 Lightning at 70 MPGe does wonders for Ford's fleet average compared to an EcoBoost F-150 at 22 mpg. And for some people converting to EVs, they want that frame of reference to a combustion vehicle or the hybrid they're migrating from.
Though mi/kWh is a more effective measure for an EV, if we did away with MPGe completely, it would be harder for consumers to compare an EV with an ICE model. Miles per kWh numbers are typically quite small (ranging from around two to four), making them far different than mpg, which can range from under 20 to well above 50. Since many consumers still cross-shop EVs and ICE vehicles, MPGe is still the best way to compare them quickly. That's why the two numbers should co-exist, creating a period of transition between them.