EV Efficiency Converter

About this calculator

An electric car's efficiency is quoted four ways, and two of them run backwards relative to the other two. km/kWh and mi/kWh count distance per unit of energy, so bigger is better. Wh/km and kWh/100 km count energy per unit of distance, so bigger is worse.

Crossing between the two families is a reciprocal: 6 km/kWh is 166.67 Wh/km, not 6,000 and not 0.006. This converter does all four and says when the direction of "better" has flipped.

How to use this calculator

1. Enter the figure you have.
2. Say which unit it is in — the car's own display will tell you.
3. Pick the unit you want.

All four are shown regardless, so you only need to be sure of what you started with.

The formula

Everything is converted through km/kWh:

  from km/kWh      x 1
  from mi/kWh      x 1.609344
  from Wh/km       1000 / value      (reciprocal)
  from kWh/100 km  100 / value       (reciprocal)

and back out the same way.

The mile factor is exact by definition. The two reciprocals carry the number their family counts over — a thousand watt-hours in a kilowatt-hour, a hundred kilometres in "per 100 km".

Worked example

6 km/kWh, written every way:

km/kWh        6
Wh/km         166.67
kWh/100 km    16.67
mi/kWh        3.73

Notes and limits

• Indian and European sources usually quote Wh/km or kWh/100 km. American ones quote mi/kWh, or MPGe, which is a different thing again and is not converted here.
• A car's trip computer reports energy leaving the battery. The energy you pay for is higher, because charging loses 10–15% between the socket and the cells.
• Efficiency figures are far more sensitive to speed and temperature than petrol mileage is. A figure without conditions attached is not comparable with another one.
• To turn an efficiency into a range, use the EV range calculator.

What this calculation assumes

• The conversion factors are exact by definition, so the conversion is exact.
• The figure describes energy at the battery, not energy off the meter.