Why Are There So Many Power Units?
Browse any car manufacturer's website and you'll encounter a confusing mix of power units: BHP, PS, HP, kW — sometimes even CV or PK. These all measure the same fundamental thing (engine power output), but they originate from different countries and engineering traditions. Knowing how to convert between them lets you accurately compare cars from different manufacturers and markets.
Understanding Each Unit
BHP — Brake Horsepower
BHP is the standard power unit used in the United Kingdom. It measures power at the engine output shaft with all standard accessories fitted. It's the figure most commonly quoted in UK car adverts, reviews, and specification sheets.
HP — Horsepower (SAE)
HP is the American standard, defined by the Society of Automotive Engineers (SAE). Since 2005, SAE has required "net" horsepower measurements (with accessories fitted), making modern HP figures virtually identical to BHP. Older HP figures were often "gross" measurements and ran higher than BHP.
PS — Pferdestärke
PS stands for Pferdestärke — German for "horse strength." It is the metric horsepower used across most of continental Europe. One PS is defined as the power needed to lift 75 kilograms by one metre in one second. PS is very close to — but not exactly the same as — BHP.
kW — Kilowatts
kW is the SI (International System of Units) measure of power. It's used in scientific contexts, by electric vehicle manufacturers, and increasingly on official EU fuel economy documents. Electric car specs are almost always quoted in kW.
Exact Conversion Factors
| From | To BHP | To PS | To HP | To kW |
|---|---|---|---|---|
| 1 BHP | — | × 1.0139 | ≈ 1.000 (modern) | × 0.7457 |
| 1 PS | × 0.9863 | — | × 0.9863 | × 0.7355 |
| 1 HP (SAE) | ≈ 1.000 (modern) | × 1.0139 | — | × 0.7457 |
| 1 kW | × 1.3410 | × 1.3596 | × 1.3410 | — |
Note: BHP and modern SAE HP are so close that for practical purposes they are interchangeable. The meaningful distinction is between BHP/HP and PS, and between both of those and kW.
Quick Conversion Examples
- 100 PS to BHP: 100 × 0.9863 = 98.6 BHP
- 200 BHP to kW: 200 × 0.7457 = 149.1 kW
- 150 kW to BHP: 150 × 1.3410 = 201.2 BHP
- 300 PS to kW: 300 × 0.7355 = 220.7 kW
- 500 BHP to PS: 500 × 1.0139 = 506.9 PS
Practical Reference Table
| BHP | PS | kW |
|---|---|---|
| 100 | 101.4 | 74.6 |
| 150 | 152.1 | 111.9 |
| 200 | 202.8 | 149.1 |
| 250 | 253.5 | 186.4 |
| 300 | 304.2 | 223.7 |
| 400 | 405.6 | 298.3 |
| 500 | 506.9 | 372.8 |
When Does the Difference Actually Matter?
For most everyday car comparisons, the difference between BHP and PS is negligible — fewer than 2% apart. However, when comparing cars across very different markets or reading older spec sheets, using the correct conversion is important for accuracy. The most significant practical difference is converting to or from kW, particularly when comparing electric vehicles (quoted in kW) against traditional petrol or diesel cars (quoted in BHP or PS).
Tips for Reading Car Specs
- UK and American spec sheets typically use BHP or HP.
- German, French, Italian, and most European manufacturers often quote PS alongside kW.
- Electric vehicle specs almost always use kW (and sometimes PS).
- When in doubt, convert everything to kW for a neutral comparison.