What is a EV Efficiency Converter?
The EV efficiency converter switches between km/kWh, Wh/km, kWh/100km, and MPGe.
How it's calculated
Wh/km = 1,000 ÷ (km/kWh)
MPGe converts 33.7 kWh as energy-equivalent to one gallon of gasoline.
Units that are easy to mix up
| Units | Why it's confusing | How to tell them apart |
|---|---|---|
| km/kWh vs Wh/km | Opposite directions | Higher is better for km/kWh, lower is better for Wh/km |
| MPGe isn't actual running cost | Mistaken for a direct cost comparison | It's an energy-equivalent metric that ignores the price gap between electricity and gasoline |
Why so many different efficiency units?
Same story as fuel economy: km/kWh is better when higher, Wh/km and kWh/100km are better when lower, and MPGe is a US metric designed to let people compare EVs to gas cars. MPGe is an energy-equivalent comparison, though — since electricity is typically far cheaper per unit of energy than gasoline, an EV with the same MPGe as a gas car will still cost much less to actually run.
Good to know
- EVs are more efficient in city driving — the opposite of gas cars — because regenerative braking recovers energy during deceleration, and the motor draws zero power while stopped.
- Cold weather significantly reduces EV range, mostly because cabin heating draws directly from the battery (gas cars get heat for free from engine waste heat). Whether a vehicle has a heat pump makes a big difference to winter range.
- EVs lose relative efficiency on the highway too, since aerodynamic drag scales with the square of speed, and EVs start from such high low-speed efficiency that the drop feels more pronounced.
- Fast charging generates more heat and loses more energy in the process compared to slow charging, and repeated fast charging can accelerate battery wear.
- Battery specs distinguish gross (total) and usable (net) capacity — manufacturers reserve a buffer at both ends to protect the battery, so a '77 kWh' battery might only deliver about 74 kWh usable.
Frequently asked questions
Q. What is 5 km/kWh in Wh/km?
200 Wh/km. Calculate as 1,000 ÷ 5.
Q. Why does range drop in winter?
Battery efficiency drops in cold temperatures, and cabin heating draws power directly from the battery.
Q. Does MPGe reflect actual running cost?
Not directly. It's an energy-equivalent comparison and doesn't account for the price difference between electricity and gasoline.