Convert kilowatts to brake horsepower at the crank, and estimate what reaches the wheels after drivetrain losses.
Sizing the electrical supply for the same machine? Use the kVA to kW calculator.
Every diagram and table on this page updates with the calculator above.
"Brake" refers to the dynamometer brake used to load the engine, not to a different unit.
Brake horsepower uses exactly the same constant as mechanical horsepower. The word "brake" is about the measurement method: the engine is loaded by a brake until it holds a steady speed, and the restraining torque is measured.
Gearbox, differential, driveshafts and bearings all absorb part of the engine output. The remainder reaches the road, and that is what a rolling road actually measures.
| Layout | Typical loss | From 200 bhp |
|---|---|---|
| Front-wheel drive, manual | 10 – 14% | 172 – 180 whp |
| Rear-wheel drive, manual | 13 – 17% | 166 – 174 whp |
| Rear-wheel drive, automatic | 16 – 20% | 160 – 168 whp |
| All-wheel drive | 20 – 25% | 150 – 160 whp |
Drivetrain drag is closer to a fixed torque than a fixed fraction, so the percentage falls as power rises. Treat any single figure as an approximation.
Engine out of the car, coupled directly to a brake. Measures true crank output with no drivetrain in the way.
Wheels removed, hubs coupled to the load. Removes tyre losses and slip, but keeps the drivetrain.
Car drives onto rollers. Convenient and repeatable, but includes tyre deformation and slip.
Numbers from the three methods are not interchangeable. Comparing a rolling-road figure with a manufacturer crank figure without accounting for the difference is the single most common mistake in this area.
Common engine outputs with wheel horsepower at your selected drivetrain loss.
| kW | Brake horsepower (bhp) | Wheel horsepower (whp) |
|---|---|---|
| 50 kW | 67.05 | 56.99 |
| 66 kW | 88.51 | 75.23 |
| 75 kW | 100.58 | 85.49 |
| 90 kW | 120.69 | 102.59 |
| 100 kW | 134.1 | 113.99 |
| 110 kW | 147.51 | 125.39 |
| 125 kW | 167.63 | 142.48 |
| 150 kW | 201.15 | 170.98 |
| 175 kW | 234.68 | 199.48 |
| 200 kW | 268.2 | 227.97 |
| 250 kW | 335.26 | 284.97 |
| 300 kW | 402.31 | 341.96 |
| 400 kW | 536.41 | 455.95 |
| 500 kW | 670.51 | 569.93 |
Air density changes with temperature, pressure and humidity, and engine output follows it. Standards exist precisely so figures can be compared across days and sites.
| Standard | Reference conditions | Notes |
|---|---|---|
| SAE J1349 | 25 °C, 990 mbar dry | Common US automotive standard |
| DIN 70020 | 20 °C, 1013 mbar | Historic European standard, slightly optimistic |
| ECE R85 | 25 °C, 1000 mbar | EU type approval |
| ISO 1585 | 25 °C, 990 mbar | Widely used internationally |
Note: Drivetrain loss is an estimate; measured losses vary with gear, temperature and tyre pressure.
Because the loss is applied as a percentage, wheel power tracks crank power in a straight line. Real drivetrains deviate slightly, with proportionally higher losses at low power.
29 calculators built on the same maths as the tool above. Each one has its own inputs, interactive diagrams and worked examples.
Common questions about converting kw to bhp.