A calculator to convert between EPA, MPGe, Wh/mi, kWh/mi, mi/kWh, Wh/km, kWh/km, km/kWh
| Unit | Value |
|---|---|
| MPGe | |
| Wh / mi | |
| kWh / mi | |
| kWh / 100 mi | |
| mi / kWh | |
| Wh / km | |
| kWh / km | |
| kWh / 100 km | |
| km / kWh |
Every unit on this page is derived from one base number, Wh/mi. The EPA defines one gallon of gasoline as 33.705 kWh of energy, and MPGe is simply how many miles a vehicle travels on that much electricity. The rest are unit conversions, so calculations work like this:
Example: 300 Wh/mi is 33,705 ÷ 300 = 112.35 MPGe, which works out to 30.00 kWh/100 mi, 3.33 mi/kWh, 186.41 Wh/km, and 5.36 km/kWh.
The same efficiency shows up as kWh/100 mi on an EPA window sticker, Wh/mi on a Tesla, and kWh/100 km in Europe. This page helps you translate between the different nomenclature used in different geographies and by different manufacturers.
1) Wh/mi (or Wh/km) provides more precision for trip planning. Wh/mi is about two to three times as precise as MPGe, and about 30 to 100 times more precise than mi/kWh (in whole-number increments). E.g., 4 mi/kWh = 250 Wh/mi, and 5 mi/kWh = 200 Wh/mi (50x more precise).
2) Wh/mi measures energy used per mile: what you buy and what the pack holds.
MPG, MPGe, and mi/kWh all put the energy in the denominator (miles per gallon, miles per 33.705 kWh, miles per kWh).
That is backwards for comparing costs and causes wildly misleading comparisons, so equal-looking jumps are not equal savings:
10 → 15 MPG saves 3.33 gal/100 mi travelled;
30 → 45 MPG saves only 1.11 gal/100 mi.
The same trap applies to EVs:
2 → 3 mi/kWh saves 16.67 kWh/100 mi;
4 → 6 mi/kWh saves only 8.33 kWh/100 mi.
With the distance as the denominator, the comparisons stay linear.
For Wh/mi: double the number, double the energy use, double the cost. Simple.
Units like mi/kWh measure distance (higher is better), while Wh/mi measures energy consumption (lower is better). When you become more efficient, your mi/kWh goes up, but your Wh/mi goes down.
Yes. Wh/km measures how much energy is used to move the car. A lower number means the car is more efficient. For example, 150 Wh/km is more efficient than 250 Wh/km.
Many of these numbers represent the same data with a shifted decimal point. For example, kWh/mi is simply Wh/mi divided by 1,000. Units like Wh/mi and Wh/km are the most "precise" because they provide whole-number granularity for trip planning, whereas others are shifted to make them easier to read or compare to manufacturer ratings.
Think of kW (Kilowatts) as speed and kWh (Kilowatt-hours) as capacity. In EV terms, kW is how fast you are charging, while kWh is the total energy your battery holds.
Yes, significantly. Efficiency units like Wh/mi or Wh/km are not static. Driving at higher speeds increases air resistance, which raises your energy consumption (higher Wh/mi) and lowers your range. If you are ever worried about reaching your destination in an EV, drop your highway speed by 10 mph and it will make an appreciable difference.
To find your estimated range, divide your battery's usable capacity (in Wh) by your efficiency. For example, if you have a 75 kWh battery (75,000 Wh) and your average efficiency is 300 Wh/mi, your estimated range is 250 miles.
Your car displays real-time efficiency based on your driving habits, weather, and terrain. This calculator provides the mathematical equivalents based on standard constants; your car shows what you are actually achieving.