kW to km/h Calculator
Estimate an electric vehicle's speed in km/h from motor power and weight.
This calculator estimates a vehicle's speed in km/h from its motor power in kilowatts and its weight — handy for electric vehicles, which are usually rated in kW rather than horsepower.
How It Works
Result in m/s; × 3.6 for km/h.
At top speed almost all the engine's output is going into pushing air aside, so the governing variable is the vehicle's drag area — its frontal area multiplied by its drag coefficient. Weight barely enters into it. That is why the body-shape selector matters more here than the weight field, which is used only for the secondary quarter-mile trap-speed figure.
How to Use This Calculator
- Enter motor power in kW.
- Enter weight in kilograms.
- Read estimated speed in km/h and MPH.
Worked Example
Why EVs Are Rated in kW
Electric vehicles quote motor output in kilowatts because it maps directly to the battery and charging system, both measured in kW and kWh. To compare an EV against a gasoline car's horsepower, convert kW to HP (×1.341) first. This calculator does that automatically, then estimates achievable speed from the resulting power-to-weight ratio.
Why Real EV Top Speed Is Often Lower
Most EVs are electronically limited well below their theoretical power-derived speed. Manufacturers cap top speed to protect range (drag rises with the cube of speed, draining the battery fast), to stay within tire and motor thermal limits, and for stability. So treat this figure as a performance-potential estimate, not a number the car will actually reach unrestricted.
Why Speed Follows the Cube Root of Power
The single most useful thing to understand here is that top speed scales badly with power — and the reason is aerodynamics.
Air resistance rises with the square of speed. But power is force times velocity, so the power needed to overcome that drag rises with the cube of speed. Invert it and speed rises only with the cube root of power:
| Power increase | Top speed increase | In practice |
|---|---|---|
| +25% | +8% | 180 → 194 km/h |
| +50% | +14% | 180 → 206 km/h |
| +100% | +26% | 180 → 227 km/h |
| +300% | +59% | 180 → 286 km/h |
This is why chasing top speed gets so expensive, and why acceleration and top speed are almost unrelated problems. Acceleration is limited by power-to-weight; top speed is limited by power against drag, where weight barely matters at all.
Smaller Power: E-Bikes, Scooters and Motorcycles
Plenty of people arrive here asking how fast 3 kW, 11 kW or 35 kW will go — figures from light electric vehicles rather than cars. Typical achieved speeds for that class:
| Motor power | Vehicle type | Typical speed | Limited by |
|---|---|---|---|
| 0.25 kW | Pedal-assist e-bike | 25 km/h | Law, not power |
| 1–2 kW | Electric scooter | 45–60 km/h | Gearing and law |
| 4 kW | Moped-class | ~45 km/h | Legally capped |
| 11 kW | A1 motorcycle | 100–120 km/h | Drag |
| 35 kW | A2 motorcycle | 150–170 km/h | Drag |
| 70 kW+ | Full-power motorcycle | 200+ km/h | Drag, often electronically limited |
Note how often the limit is regulatory rather than physical. E-bikes and mopeds stop at their legal cap with power to spare. For motorcycles, the 11 kW and 35 kW figures are the EU A1 and A2 license ceilings — see motorcycle power-to-weight for the full rules, which also cap power-to-weight ratio.
Drag-Limited Speed by Power and Body Shape
Potential top speed in km/h before any electronic limiter, by drag area. Note how much more the body shape matters than the power.
| Motor power | Approx. hp | Sports car Cd·A 0.55 | Sedan / EV Cd·A 0.65 | Hatchback Cd·A 0.72 | SUV Cd·A 0.85 |
|---|---|---|---|---|---|
| 50 kW | 67 | 183 | 173 | 167 | 158 |
| 75 kW | 101 | 209 | 198 | 191 | 181 |
| 100 kW | 134 | 230 | 218 | 210 | 199 |
| 150 kW | 201 | 263 | 249 | 241 | 228 |
| 200 kW | 268 | 290 | 274 | 265 | 251 |
| 250 kW | 335 | 312 | 295 | 286 | 270 |
| 400 kW | 536 | 365 | 346 | 334 | 316 |
These are unrestricted drag-limited potentials, not figures road cars reach. Manufacturers cap top speed well below them — commonly 180 km/h on an EV — to protect range, stay inside tire speed ratings and motor thermal limits, and because a single-speed transmission runs out of motor rpm. A 250 kW EV limited to 200 km/h is not underperforming; it is doing what it was designed to do.
Frequently Asked Questions
Convert kilowatts to horsepower (×1.341), then estimate speed from the power-to-weight ratio. The calculator does both steps automatically.
Kilowatt is the SI unit for power and is standard for electric motors worldwide. Many makers also quote the horsepower equivalent for familiarity.
Not necessarily. Many EVs are electronically limited below their theoretical maximum to protect range, motor, and tires.
About 201 mechanical horsepower, since 1 kW equals roughly 1.341 HP.
Through power-to-weight, yes, especially in acceleration. At high speed, aerodynamic drag becomes the dominant factor.
Both are searched. If you meant road speed, this page. If you meant KM — koń mechaniczny, Polish for metric horsepower, also KS in Croatia and Serbia — use kW to PS, where 1 kW = 1.36 KM.
Drag rises with the square of speed, so the power to overcome it rises with the cube. Speed therefore follows the cube root of power — doubling power buys about 26% more speed, and doubling speed needs roughly eight times the power.
In a motorcycle, roughly 150–170 km/h — 35 kW is the EU A2 license ceiling. In a 1,400 kg car it would be far slower, around 130 km/h, because the car pushes a much larger hole through the air.
Most EVs are electronically limited well below their power-derived potential — to protect range, stay inside motor and tire thermal limits, and because single-speed transmissions run out of motor rpm. The cap is a design choice, not a power limit.
Aerodynamics, almost entirely. Weight dominates acceleration, but at top speed it barely matters — a heavy slippery sedan will out-run a light boxy van of identical power. This calculator uses weight as a class proxy, which is why it is an estimate.