kWh per 100 Miles: How to Read EV Efficiency

kWh per 100 miles tells you how many kilowatt-hours of electricity an electric vehicle uses to travel 100 miles, so a lower number means a more efficient vehicle. It is the electric equivalent of gallons per 100 miles, and it is printed on the EPA label next to MPGe. Of the two, kWh per 100 miles is the better guide to running cost.

Key takeaways

• On the EPA label, the kWh per 100 miles value tells you how many kilowatt-hours the vehicle would use to travel 100 miles.
• Lower kWh per 100 miles is better, the opposite direction from MPGe, where higher is better.
• The measurement includes charging losses, so it reflects energy drawn from the outlet rather than energy that reaches the battery.
• To estimate cost, multiply by your electricity price per kWh. Prices are set by your utility or charging network, not by the EPA.

What the number means

A kilowatt-hour (kWh) is a unit of electrical energy. The EPA’s electric label and plug-in hybrid label both state that kWh per 100 miles tells you how many kilowatt-hours the vehicle would use to travel 100 miles. A vehicle at 30 kWh per 100 miles uses 0.30 kWh for each mile, so 15,000 miles would use 4,500 kWh.

Many drivers also meet this number as its inverse, miles per kWh, in other places. The EPA label uses kWh per 100 miles because, like gallons per 100 miles, it adds up the way a bill does: twice as much energy per 100 miles is twice the energy purchased.

Relationship to MPGe

MPGe converts the same energy use into gasoline-gallon terms using 33.7 kWh per gallon. Using that definition:

MPGe = 3,370 / (kWh per 100 miles), approximately.

kWh per 100 miles	Approximate MPGe
25	135
30	112
35	96
40	84

The EPA’s test procedure documents state a conversion factor of 33.705 kWh per gallon, which is where the rounded 33.7 comes from. The pairs above are rounded arithmetic, not EPA ratings of any vehicle, and other unit conversions are in MPG to L/100 km and other conversions. For more on the unit, see what is MPG and MPGe.

What is included in the number

EPA testing recharges the battery after the test drive and divides the recharge energy by the miles traveled. According to the EPA’s test procedure summary, the recharge energy includes any losses due to inefficiencies of the manufacturer’s charger. The EPA’s MPGe values include charging losses and assume Level 2, alternating-current charging, and the label values are adjusted so that they better reflect what customers can expect in the real world; see how the EPA tests fuel economy.

That matters for cost. Energy that never reaches the battery still shows up on your electricity meter, so a figure that includes charging losses is the right base for a cost estimate.

From efficiency to running cost

The arithmetic is short:

annual electricity cost = miles per year x (kWh per 100 miles / 100) x price per kWh

At 15,000 miles and 30 kWh per 100 miles, the vehicle uses 4,500 kWh, so each 1 cent per kWh of electricity price is $45 a year. A vehicle at 25 kWh per 100 miles uses 3,750 kWh, or $37.50 for the same 1 cent. Your electricity price varies by utility, state, season and time of day. Public charging can differ from home charging, covered in home vs public EV charging costs. The EIA publishes average residential electricity prices by state; the fuel cost by state pages use them. The EV vs gas calculator puts both fuels on the same footing.

Why efficiency changes in daily use

Efficiency is not a fixed property. fueleconomy.gov reports that, in cold weather, an EV’s fuel economy can drop roughly 39% in mixed city and highway driving, and Department of Energy research identifies power for cabin heating and cooling as the primary reason. Speed, load, tires and terrain matter too. See EV range explained for how these factors affect how far a charge goes.

Efficiency is not the same as size or range

A small battery in an efficient car and a large battery in a less efficient car can have the same range. Efficiency (kWh per 100 miles) and battery capacity (kWh) are separate numbers; range is roughly capacity divided by consumption. When comparing electric cars, check both, and compare plug-in options using hybrid vs plug-in hybrid vs EV.