Buyer Guides
Car Power Metrics: Understanding kW, PS, BHP, and Mechanical HP
By Automotive Analyst • Published August 19, 2026
Car Power Metrics: kW, PS, BHP, and HP Compared
When reading car specifications across international automotive publications, you will encounter multiple units for engine output. While they all quantify the rate at which work is performed, their reference systems and test conditions differ.
The Four Major Power Units
1. Kilowatt (kW)
- Standard: International System of Units (SI).
- Usage: Official metric in European vehicle registration documents since Directive 80/181/EEC.
- Formula: 1 kW = 1,000 Joules per second.
2. Pferdestärke (PS)
- Standard: DIN 66036 (German Metric Horsepower).
- Usage: Continental Europe (Germany, Austria, Switzerland, etc.).
- Formula: 1 PS = 735.49875 Watts.
3. Mechanical / Imperial Horsepower (hp)
- Standard: SAE J1349 (US / Imperial).
- Usage: United States, Canada.
- Formula: 1 hp = 745.69987 Watts (approximately 1.01387 PS).
4. Brake Horsepower (BHP)
- Standard: Engine dyno output measured directly at the flywheel without drivetrain losses.
- Usage: United Kingdom and Commonwealth nations.
Quick Comparison Table
To compare a standard 100 kW output:
- 100 kW = 135.96 PS (Metric)
- 100 kW = 134.10 hp (Mechanical)
Understanding this 1.4% variance between PS and mechanical HP ensures you evaluate car specs accurately regardless of regional source.