Key facts
- Lower Wh/km or kWh per distance means lower consumption; higher mi/kWh means more distance per energy.
- 18 kWh/100 km equals 180 Wh/km, 28.968192 kWh/100 miles and approximately 3.452 mi/kWh.
- Combined consumption is total energy divided by total distance, with the appropriate scale factor.
- Converting units does not remove charging losses or convert EPA testing into WLTP testing.
18 kWh/100 km equals 180 Wh/km, about 28.97 kWh/100 miles and 3.45 mi/kWh. These are different units for the same energy-and-distance relationship. The conversion is valid only when the underlying measurement stays the same: a unit calculator cannot turn battery energy into wall-meter energy or convert one official test procedure into another.
Use the formulas below to compare international specifications, rental-car displays or your own journey records. All worked trip figures are hypothetical. The conversion constants are fixed; the driving results you enter depend on their source.
Which direction means better efficiency?
| Unit | Question it answers | Better direction for comparable measurements |
|---|---|---|
| Wh/km | How many watt-hours for one kilometre? | Lower |
| kWh/100 km | How many kilowatt-hours for 100 kilometres? | Lower |
| kWh/100 miles | How many kilowatt-hours for 100 miles? | Lower |
| mi/kWh | How many miles for one kilowatt-hour? | Higher |
For regional context, Canada’s EnerGuide battery-electric label uses kWh/100 km, while the U.S. FuelEconomy.gov label explanation describes kWh/100 miles. Those regional examples explain the different presentation; they do not make the test results interchangeable.
The conversion formulas
Use 1 mile = 1.609344 kilometres and 1 kWh = 1,000 Wh. NIST’s official conversion tables give the international-mile conversion and energy-unit factors. The formulas below follow directly from those unit relationships.
| From | To | Calculation |
|---|---|---|
| Wh/km | kWh/100 km | Divide by 10 |
| kWh/100 km | Wh/km | Multiply by 10 |
| kWh/100 km | kWh/100 miles | Multiply by 1.609344 |
| kWh/100 miles | kWh/100 km | Divide by 1.609344 |
| kWh/100 miles | mi/kWh | 100 ÷ the input |
| mi/kWh | kWh/100 miles | 100 ÷ the input |
| kWh/100 km | mi/kWh | 100 ÷ (1.609344 × the input) |
| mi/kWh | Wh/km | 1,000 ÷ (1.609344 × the input) |
For example, 180 Wh/km × 100 km is 18,000 Wh, or 18 kWh. Multiplying 18 by 1.609344 gives 28.968192 kWh/100 miles. Taking 100 ÷ 28.968192 gives about 3.452 mi/kWh. Keep the full value during calculation and round the final display.
Use your own figures
EV efficiency unit converter
Convert the same energy-and-distance measurement into four common units. Conversion does not turn a battery-side reading into wall electricity, or one test cycle into another.
Formula and worked example
One mile is exactly 1.609344 km. Starting with C kWh/100 km: Wh/km = 10 × C; kWh/100 miles = 1.609344 × C; miles/kWh = 100 ÷ (1.609344 × C).
For example, 18 kWh/100 km = 180 Wh/km ≈ 28.9682 kWh/100 miles ≈ 3.4521 miles/kWh. These are the same illustrative measurement, rounded for display.
Lower Wh/km or kWh/100 distance means less energy per distance; higher miles/kWh means more distance per energy. Keep the vehicle, trip conditions and energy measurement boundary comparable. For several trips, add the distances and energies first, then form the ratio required by the chosen unit rather than averaging the displayed ratios.
A quick comparison table
Every row describes one equivalent consumption rate, rounded to two decimal places where useful. These are reference calculations, not model ratings or a ranking of what an EV should achieve.
| Wh/km | kWh/100 km | kWh/100 miles | mi/kWh |
|---|---|---|---|
| 120 | 12 | 19.31 | 5.18 |
| 150 | 15 | 24.14 | 4.14 |
| 180 | 18 | 28.97 | 3.45 |
| 200 | 20 | 32.19 | 3.11 |
| 250 | 25 | 40.23 | 2.49 |
A common error is to see a larger mi/kWh number and treat it as larger consumption. It means more distance per unit of energy. For example, 4 mi/kWh converts to 25 kWh/100 miles, while 3 mi/kWh converts to about 33.33 kWh/100 miles.
Combine trips using total energy and total distance
Converting the units correctly does not guarantee a correct average. Suppose a hypothetical first leg covers 100 km at 18 kWh/100 km, and a second covers 300 km at 24 kWh/100 km.
| Leg | Distance | Consumption | Calculated energy |
|---|---|---|---|
| A | 100 km | 18 kWh/100 km | 18 kWh |
| B | 300 km | 24 kWh/100 km | 72 kWh |
| Total | 400 km | 22.5 kWh/100 km | 90 kWh |
The combined rate is 100 × 90 ÷ 400 = 22.5 kWh/100 km. Simply averaging 18 and 24 gives 21 and understates the total because the higher-consumption leg is three times longer.
Reciprocal units need particular care. Two hypothetical 100-mile legs at 4 mi/kWh and 2 mi/kWh use 25 kWh and 50 kWh. Combined economy is 200 ÷ 75 = 2.67 mi/kWh, approximately, rather than the simple average of 3. Add the actual distances and energies first; divide afterward.
A unit change cannot fix a measurement-boundary mismatch
Imagine a documented battery-energy result of 180 Wh/km and a separate wall-meter result of 20 kWh/100 km for matching travel and recharge intervals. Converting the first gives 18 kWh/100 km, so the figures still differ. That is not a conversion error: the measurements include different parts of the energy path.
The U.S. EPA explicitly says its MPGe calculation accounts for charging losses under Level 2 AC charging assumptions, bringing the measurement to the electrical outlet. See EPA’s fuel-economy and EV-range testing explanation. A vehicle display may describe another measurement boundary; check its documentation instead of assuming an identical definition.
For purchased-electricity budgeting, use an appropriate supply-energy measurement and the matching tariff. For a battery-energy travel budget, keep the battery-side consumption basis consistent. Do not add an assumed charging-loss percentage again to a figure that already includes it. Our wall-versus-battery energy guide explains how to document the distinction.
Check these five details before comparing two numbers
- Units: distinguish km from miles, Wh from kWh, and energy per distance from distance per energy.
- Measurement point: identify wall supply, charger billing point, battery data or an undocumented display estimate.
- Interval: compare matching journeys and accounting periods; avoid mixing a short leg with an entire month.
- Test or conditions: identify the official procedure or actual trip conditions behind each result.
- Precision: calculate from original values where available, then round once.
Unit conversion does not transform EPA ratings into WLTP ratings; our EPA-versus-WLTP guide addresses that separate comparison. For MPGe and the rest of the U.S. label, use our EV window-sticker guide.
Apply consistent units when estimating range with a roof box or rear carrier or comparing per-minute and per-kWh charging prices.
Frequently asked questions
Is 200 Wh/km the same as 20 kWh/100 km?
Yes. Multiply 200 Wh by 100 kilometres, then divide 20,000 Wh by 1,000 to get 20 kWh. The measurement basis must remain the same.
Can I convert kW into mi/kWh?
Not from kW alone. Power is energy per time, while mi/kWh relates distance to energy. You also need compatible distance and energy information for the interval.
What should I do with a zero or negative short-trip reading?
The reciprocal formulas are intended for positive consumption values. A zero denominator is undefined; a negative net reading is unsuitable for these ordinary comparison tables. Use a representative, documented interval instead of interpreting the result as a normal consumption rating.
Source review: 12 November 2026. Regional label examples are explicitly identified. Tables and trip averages are original calculations, not manufacturer claims or first-hand driving measurements.
