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.
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.
