kWh and Miles per kWh: EV Efficiency Explained

Gas cars gave you one efficiency number — miles per gallon — and everyone learned to read it. EVs have three units in circulation and none of them are intuitive at first. Once you can move between them, range estimates and charging costs stop being mysterious.

What is a kWh?

A kilowatt-hour (kWh) is energy: one kilowatt of power sustained for one hour. It's what your utility bills, what your battery stores, and what a charging session delivers.

Two related units cause confusion:

• kW (kilowatt) is power — a rate. Your charger's 11.5 kW is how fast it moves energy.
• kWh (kilowatt-hour) is energy — an amount. Your battery's 75 kWh is how much it holds.

Power times time equals energy. An 11.5 kW charger running for two hours delivers about 23 kWh, minus losses. That relationship is the backbone of every charging-time and charging-cost calculation, including the EV charging time calculator.

What is a good miles per kWh?

Miles per kWh is the EV analogue of miles per gallon: how far you travel per unit of energy. Most passenger EVs land somewhere around 3 to 4 mi/kWh in mixed driving. Aerodynamic compacts do better; full-size electric trucks and three-row SUVs do worse.

Two things make it useful:

Range prediction. Usable battery capacity times miles per kWh equals range. A 75 kWh pack at 3.5 mi/kWh is roughly 260 miles — and it moves with the seasons in a way a fixed EPA number never will.

Cost per mile. Divide your electricity rate by your miles per kWh. At a rate of $0.16/kWh and 3.5 mi/kWh, that's about 4.6 cents per mile before charging losses. Compare that against a gas car's cost per mile and the gap is usually dramatic — the EV vs gas cost calculator does the full comparison.

What is kWh per 100 miles?

The EPA window sticker uses kWh/100 mi, which runs the other direction — lower is better. It's the same information inverted:

kWh/100 mi = 100 ÷ miles per kWh

So 3.5 mi/kWh is about 28.6 kWh/100 mi. The advantage of this form is that it scales linearly with cost, which makes comparing two vehicles less deceptive than the miles-per-unit form (the same trap as MPG).

What is MPGe?

MPGe — miles per gallon equivalent — exists so buyers can compare an EV to a gas car on a familiar scale. The EPA sets one gallon of gasoline as equivalent to 33.7 kWh of electricity.

MPGe = miles per kWh × 33.7

At 3.5 mi/kWh that's about 118 MPGe. It's a fair energy comparison, but it says nothing about money — electricity and gasoline aren't priced per unit of energy, so a high MPGe doesn't automatically mean low cost, and a driver in a high-rate market can pay more per mile than a driver in a low-rate one with the same car. Electricity rates by state shows how much that varies.

Quick conversion table

What affects EV efficiency?

Your real number is not a constant. The main drivers:

Speed. Aerodynamic drag rises with the square of speed, and the power needed to overcome it rises with the cube. Highway driving at 75 mph is meaningfully less efficient than at 65 — this is the single largest controllable factor on a road trip.

Temperature. Cold hurts twice: the battery is less efficient when cold, and cabin heating draws real power because there's no waste engine heat to borrow. Winter efficiency drops are normal and often substantial. See cold-weather EV charging.

Climate control. Heating costs more than cooling in most EVs. Heat pumps reduce the penalty; resistive heaters don't.

Terrain and load. Climbing costs energy; regenerative braking gives some of it back on the way down, but not all. Cargo, roof boxes and passengers all take their cut — a roof box is a large aerodynamic penalty at highway speed.

Tires. Tire choice and inflation matter more on EVs than most people expect. Underinflated or aggressive-tread tires cost range every mile.

Turning efficiency into cost

The whole chain, in one line:

Cost per mile = electricity rate ÷ (miles per kWh × charging efficiency)

Charging efficiency accounts for energy lost between the meter and the battery — conversion losses in the onboard charger, cable resistance, and thermal management. Level 2 charging is reasonably efficient; Level 1 is noticeably worse because fixed overhead is spread over less delivered energy. See how EV charging works for why.

For a monthly figure rather than a per-mile one, EV charging cost per month walks through the arithmetic, and the monthly EV charging cost calculator does it for you.

How to find your own number

Don't trust the sticker — measure:

1. Use the car's lifetime efficiency display if it has one. That's your true long-run average.
2. Reset a trip meter at the start of a typical week and read the average at the end.
3. Track it seasonally. Summer and winter numbers will differ, and you want both for planning.
4. Use the winter number for range planning and the annual average for cost planning.

Once you have it, everything else follows: range is capacity times efficiency, cost is rate divided by efficiency, and charging time is energy needed divided by charging power.

The bottom line

kWh is the currency of EV ownership. Miles per kWh converts it to distance, kWh/100 mi converts it to cost, and MPGe converts it to a gas-car analogy. Learn your own real average in both seasons and you can predict range and cost more accurately than any sticker.

Price your own driving with the EV charging cost calculator, estimate range with the EV range calculator, or look up cost to charge by model.