Views: 69 Author: Site Editor Publish Time: 2026-07-11 Origin: Site
Based on ISO standards and international engineering practice, the definitions and conversions for engine power units are as follows.
### ⚙️ ISO Definitions of Power Units
The SI (International System of Units) unit for power is the Watt (W), with kilowatt (kW) being the most commonly used multiple in engine specifications.
- Kilowatt (kW): The coherent SI unit for power, defined as 1 kJ/s. ISO 80000-4 is the primary standard for defining SI units in mechanics.
- Horsepower (hp): A non-SI unit. In engine standards, "hp" typically refers to Mechanical (Imperial) Horsepower, defined as exactly 550 ft·lbf/s.
- PS (Metric Horsepower): A non-SI unit derived from the metric system. Defined as 75 kgf·m/s, it's expressed in standards like ISO 1585 and ISO 2534.
Key ISO standards referencing these units include ISO 15550 (framework), ISO 3046-1 (performance), ISO 1585 (net power), ISO 2534 (gross power), and ISO 80000-4 (SI units).
### Conversion Calculations
1 hp (imperial horsepower) ≈ 0.7457 kW, or 1 kW ≈ 1.341 hp.
1 PS (metric horsepower) ≈ 0.7355 kW, or 1 kW ≈ 1.360 PS.
1 hp ≈ 1.015 PS (1.5 % difference).
