What Does an EV Battery’s Miles per KWh Number Mean?

Miles per kilowatt-hour is a term you may have heard in connection to electric vehicles (EVs). You might also have heard related terms tossed around, like kilowatt, miles-per-gallon equivalent (MPGe), and kilowatt-hours per 100 miles (kWh/100 miles). These terms all refer to the energy, in the form of electricity, that an EV uses when you drive it. 

If you’re used to gasoline-powered vehicles, these terms might seem like a lot to take in, but understanding an EV battery’s miles-per-kWh, MPGe, and kWh/100 miles numbers and what they mean isn’t hard once you get used to the terms. 

When you do, you’ll quickly see how they will help you understand how efficient an EV is, and how to compare EVs and internal combustion engine (ICE) vehicles in a meaningful way.

What kW (Kilowatt) and kWh (Kilowatt Hours) Mean

Kilowatt and kilowatt-hour are two important terms to know related to EVs; they will help you understand how an EV stores and uses energy.

Kilowatt (kW) is a measurement of energy transfer. To elaborate a bit more, the term kilowatt describes the rate at which energy flows. In the same way a term like ‘gallons per minute’ can be used to describe the rate that a liquid like water or gas flows from a hose, pump, or faucet, kilowatts describe the rate of energy transfer. A higher kW number means more energy flow, which is why your EV charges faster at higher kW charging stations. 

Kilowatt-hour (kWh) is a quantity of electricity. A kilowatt-hour is the amount of energy transferred in one hour, so it describes an amount of energy. You can think of kilowatt-hours in sort of the same way you think about gasoline: The amount of kilowatt-hours stored in an EV battery is similar to the amount of gallons of gas held in the tank of an internal combustion engine (ICE) vehicle: With either one, you can store and use them to generate power to get and keep your vehicle moving. 

How Many Kilowatt-hours EVs Use Per Mile 

As a driver, you’re going to be mainly concerned with the range and efficiency of your EV. To determine those things, you need to know how much energy an EV uses in relation to how far it travels. This is usually expressed in kilowatt-hours per mile, which is how much power the EV requires to travel one mile. 

Since different EVs have different battery sizes, performance standards, and power consumption requirements, look at how much energy each one takes to travel a given distance when you are comparing electric vehicles. This measurement is standardized, so you can just look at the kWh/100 miles ratings of two vehicles to see how efficient each vehicle is at using its battery power.

Where MPGe Fits In

In addition to the kWh/100 miles rating, the EPA also provides a miles-per-gallon equivalent rating called MPGe. Unlike the kWh/100 miles rating, which just looks at how much energy each vehicle takes to move a specific distance, MPGe is meant to help you compare the efficiency of EVs to gasoline-powered vehicles.

When the EPA establishes an MPGe for a vehicle, they start from the baseline assumption that one gallon of gas is equal to 33.7 kWh of electricity. They then look at how far a vehicle can travel using 33.7 kWh of electricity. If a vehicle uses 33.7 kWh of energy to travel 200 miles, then that vehicle receives a 200 MPGe rating, while a vehicle that travels only 100 miles using that same amount of energy would receive a 100 MPGe rating.

Shopping for EVs? How to Read the EV Windows Sticker Mileage Numbers

When you shop for a new car of any kind, you’ll see a large window sticker that offers lots of details about the car, from equipment to mileage information. 

Window sticker mileage numbers are more detailed on EVs than they are on gasoline-powered vehicles. They feature an MPGe number prominently, but you’ll also see a kWh/100 miles number, driving range numbers, fuel cost and savings numbers, and more.

The MPGe number on an EV window sticker is there to help you compare the fuel economy of that vehicle to an equivalent gas-powered vehicle. For example, a gas-powered vehicle might be able to travel 14 miles on one gallon of gas, or 14 MPG, while an EV of a similar size and design might be able to travel 119 miles using an equivalent amount of electricity, or 119 MPGe.

The more important number to look at is the kWh per 100 miles. While MPGe is useful in comparing EVs to gas-powered vehicles, it uses a conversion factor that can make it difficult to understand exactly how much electricity the EV is going to use. The kWh per 100 miles number is much simpler because it literally tells you how many kilowatt-hours the vehicle consumes to travel 100 miles.

Since the price of electricity on your power bill is expressed in kWh, the kWh per 100 miles metric makes it exceedingly easy to see, at a glance, how much a vehicle will actually cost to charge. For example, if electricity costs 12 cents per kWh where you live, and you bought a vehicle with a 30 kWh per 100 miles rating, you could expect it to cost you about $3.60 worth of electricity to drive 100 miles.

The numbers aren’t quite as simple as that in reality, of course, since chargers aren’t 100 percent efficient, and the amount of electricity your vehicle consumes will depend on a variety of environmental factors and your personal driving style. Still, it’s an easy baseline to use when you are comparison shopping.

Range vs. Efficiency: Don’t Confuse the Two

Range is one of the biggest selling points you’ll see when you shop for EVs. Since charging an EV takes longer than fueling a gasoline-powered vehicle, and there are still places where it’s difficult to find a charging station, range is an important factor to anyone who drives long distances on a regular basis. 

However, it’s important to understand that range and efficiency are very different, and a vehicle bragging about a long range doesn’t mean that it’s also as efficient or more affordable to operate than an electric vehicle that has a shorter range.

The range of an EV is just how far it can travel between charges, while the efficiency of an EV refers to how good it is at turning stored energy into range. The kWh per 100 miles rating of an EV is an efficiency rating because it shows how much energy it takes the vehicle to travel 100 miles. The range rating of an EV doesn’t address efficiency, as it just shows how far the vehicle can travel on a single charge without considering how much energy it takes to do that.

Here’s an example: If one vehicle has a 100 kWh battery and a range of 300 miles, and a second vehicle has a 20 kWh battery and a range of 60 miles, both vehicles have the same efficiency. Even though one can go much further between charges, they both take the same amount of energy to travel an equal distance. (Ed. note: In this specific example, both vehicles would have a rating of 33.3 kWh per 100 miles.)

With everything else being equal in terms of driving style and conditions, two vehicles that have different ranges but the same efficiency will cost about the same amount to operate. The main exception is that some charging stations assess a per-session fee in addition to a time-based or kWh-based fee.

If you’re paying a per-session fee, then a vehicle that doesn’t have to be charged as often will cost less to charge, over time, than a vehicle with a smaller battery that has to be charged more often.

Living With the New MPG (MPGe)

The variety of terms and numbers that get thrown around in reference to EV batteries can seem daunting, but they’re all useful. 

MPGe is also a good number to look at when comparing the efficiency of an EV to the efficiency of an ICE vehicle, while a vehicle’s kWh/100 miles rating makes it easy to see how much the vehicle will actually cost to charge and drive. Kilowatt is an important term to understand when considering how fast a charging station will work, while looking at the kWh rating of a battery is like looking at how many gallons a gas tank can hold. 

When you think about how EVs consume energy the same way ICE vehicles burn gasoline, it all makes a lot more sense.