You have kilowatts from a meter, datasheet, or drive display—now you need horsepower for a motor match or pump curve. This guide shows how to calculate horsepower from kilowatts step by step using the mechanical hp constant.
Benefits
- Single-step calc: HP = kW ÷ 0.7457.
- Worked examples from common motor and inverter kW ratings.
- Reverse check: kW = HP × 0.7457 before quoting equipment.
How it works
- Identify real power in kW—shaft, output, or measured load (not kVA).
- Divide by 0.7457 to calculate mechanical horsepower.
- Round to catalog hp steps (5, 7.5, 10, 15 hp) for procurement.
FAQ
How do I calculate horsepower from kilowatts?
HP = kW ÷ 0.7457. Example: 11.2 kW → 11.2 ÷ 0.7457 ≈ 15.02 hp—round to a 15 hp motor class. For 5.6 kW: 5.6 ÷ 0.7457 ≈ 7.51 hp, matching a standard 7.5 hp frame.
Can I calculate hp from three-phase kW?
Yes—when the kW value is already real power (not kVA), the same formula applies. A three-phase 460 V motor drawing 14 kW shaft-equivalent power is 14 ÷ 0.7457 ≈ 18.8 hp. Use measured or nameplate kW, not line voltage alone.
What if my kW includes motor losses?
Input electrical kW is higher than shaft hp/kW when efficiency is below 100%. To calculate shaft horsepower from electrical kW, multiply kW by motor efficiency first, then divide by 0.7457. Example: 10 kW electrical at 90% efficiency → 9 kW shaft → 12.07 hp.
Technical specifications
- HP = kW ÷ 0.7457 (mechanical).
- Shaft kW = electrical kW × efficiency (when needed).
- Standard NEMA hp steps: 1, 1.5, 2, 3, 5, 7.5, 10, 15, 20, 25, 30…
- Related: kw-to-hp-converter, convert-kilowatts-to-mechanical-horsepower.
One division answers most motor cross-reference questions
Given any trustworthy kW figure—VFD display, power analyzer, or inverter continuous rating—horsepower is kW divided by 0.7457. Calculating hp from kW is faster than hunting conversion tables and avoids transcription errors on bid sheets. Document the source kW (input vs. output) so reviewers know whether efficiency was already applied.
Map calculated hp to standard frame sizes
Raw results rarely land exactly on catalog steps. 7.51 hp maps to 7.5 hp NEMA frames; 18.8 hp may require a 20 hp class or a 15 hp with service factor headroom—application dependent. Calculate horsepower from kilowatts first, then apply manufacturer tables and service-factor policy rather than rounding down blindly.
Chain the calc into electrical planning
After hp is known, return to kW for breaker and wire work—hp does not replace ampacity math. For generator or UPS paths, convert kVA to kW with power factor before calculating hp. For branch circuits, follow hp → kW → amps at your line voltage when nameplates omit FLA.