MPGe calculator

What is MPGe?

Miles per gallon equivalent. The EPA counts 33.7 kilowatt-hours of electricity as the energy in one gallon of gasoline, so an EV that uses 33.7 kWh to go 100 miles is rated 100 MPGe.

How do I convert kWh/100 mi to MPGe?

MPGe = 3,370 ÷ kWh per 100 miles. 30 kWh/100 mi is 112.3 MPGe; 25 kWh/100 mi is 134.8 MPGe.

Does MPGe include charging losses?

Yes — the EPA says the MPGe values on labels include charging losses.

Is MPGe the cost to drive?

No — it compares energy use. Cost depends on your electricity price: the calculator multiplies kWh per 100 miles by your rate and compares it with a gas car at your gas price.

Which number should I compare?

For cost, kWh per 100 miles is the more useful figure: lower is better, and it multiplies directly by the price per kWh.

Worked example: from kWh per 100 miles to cost and back

An EV that uses 28 kWh per 100 miles is rated 3,370 ÷ 28 = 120.4 MPGe. At $0.17 per kWh, 100 miles cost 28 × 0.17 = $4.76. A gasoline car at 30 mpg and $3.50 a gallon needs 100 ÷ 30 = 3.33 gallons, or $11.67. Over the 15,000 miles a year that the fuel economy label assumes, that is 4,200 kWh ($714.00) against 500 gallons ($1,750.00). To go the other way, a rating of 135 MPGe means 3,370 ÷ 135 = 25.0 kWh per 100 miles. The prices here are examples; enter your own.

Where does 33.7 come from?

The EPA treats a gallon of gasoline as 115,000 Btu of energy, which equals 33.7 kWh. The MPGe rating is therefore the distance an EV travels on 33.7 kWh. The fueleconomy.gov label page defines MPGe as the miles a vehicle can go on a quantity of fuel with the same energy content as a gallon of gasoline. The label’s kWh per 100 miles is an estimated rate of consumption, and the combined figure weights city driving 55% and highway driving 45%. The annual fuel cost on a label is based on 15,000 miles a year and a projected electricity price, with the price taken from Energy Information Administration projections.

What about charging efficiency?

Not all the electricity drawn from the wall reaches the wheels. The Department of Energy’s fueleconomy.gov says EVs convert over 77% of the electrical energy from the grid to power at the wheels, and that battery charging efficiency is often 84% to 93%. For a car that uses 28 kWh per 100 miles at the battery, the wall would then supply roughly 30 to 33 kWh. The EPA says label values include charging losses. If your own consumption figure is measured at the battery rather than at the wall, multiply it by about 1.08 to 1.19 before applying your electricity price.

Common mistakes with MPGe

Reading MPGe as dollars: it measures energy, and the cost per mile also depends on the price per kWh, which differs between home charging and public chargers. Dividing when you should multiply: more kWh per 100 miles means a lower MPGe, not a higher one. Comparing MPGe with a gasoline car’s mpg for the same trip without checking prices. Forgetting that driving style, cold weather and speed change real consumption from the label’s estimate. And mixing kWh per mile with kWh per 100 miles: multiply a per-mile figure by 100 first.

Sources and related calculators

Sources: U.S. Department of Energy and EPA, fueleconomy.gov, “Electric vehicle label” explanation (MPGe, kWh per 100 miles, 55/45 city-highway weighting, 15,000-mile cost basis) and the “Electric Vehicles” technology page (charging and drivetrain efficiency); EPA conversion of 115,000 Btu per gallon to 33.7 kWh. Related: EV vs gas calculator, EV charging calculator, electricity cost calculator and fuel cost calculator.