Mechanical horsepower is a fixed SI-derived unit—745.7 watts exactly—not the same as metric PS on some import labels. This guide shows how to convert kilowatts to mechanical horsepower for US industrial equipment, VFD matching, and nameplate cross-checks.
Benefits
- Mechanical hp = kW ÷ 0.7457 (exact definition: 550 ft·lbf/s).
- Separates US mechanical hp from metric PS (≈ 0.7355 kW).
- Aligns inverter kW ratings with NEMA hp class motors.
How it works
- Take real shaft or electrical power in kilowatts (kW).
- Divide by 0.7457—the kW equivalent of one mechanical horsepower.
- Read mechanical hp for catalogs, motor stamps, and load comparisons.
FAQ
How do I convert kilowatts to mechanical horsepower?
Mechanical HP = kW ÷ 0.7457. Example: 3.73 kW → 3.73 ÷ 0.7457 = 5.0 hp mechanical. The constant comes from 745.7 W per hp. Do not use 0.7355—that is metric horsepower (PS), not mechanical.
Why is mechanical horsepower 0.7457 kW?
One mechanical horsepower is defined as 550 foot-pounds per second, which equals 745.699872 W—rounded to 745.7 W or 0.7457 kW in practice. NEMA, IEEE, and US pump curves use this definition. European DIN horsepower (PS) is slightly smaller.
Does efficiency change the kW-to-hp conversion?
The conversion factor is unit math only—hp and kW describe the same power magnitude. Motor efficiency affects how many electrical kW you draw to deliver a given shaft hp, but converting 7.5 kW shaft power still yields ~10.06 mechanical hp regardless of efficiency.
Technical specifications
- Mechanical HP = kW ÷ 0.7457.
- 1 mechanical hp = 745.7 W = 0.7457 kW.
- Metric PS: kW ÷ 0.7355 (different unit—not mechanical hp).
- Related: kw-to-hp-converter, kva-to-kw, inverter-sizing.