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Horsepower to kW Calculator

Convert motor horsepower into kilowatts for metric motor selection, cabling and supply paperwork.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Mechanical output

3.73 kW

High confidence

Converted using an exact defined factor of 0.745699872 kW per hp. This is shaft output. Electrical input is higher — divide by the motor's efficiency to get the draw.

Conversion factor applied
0.75 kW per hp

Plant and machinery bought from American suppliers arrives rated in horsepower while the electrical design around it works in kilowatts, so pump, compressor and machine-tool selection routinely needs this step. Two details cause real errors. The first is which horsepower: mechanical horsepower is 745.6999 W, but metric horsepower — still quoted on some European equipment as PS or CV — is 735.49875 W, roughly 1.4% adrift. The second is that horsepower describes what leaves the shaft, not what enters the terminals. A motor is not perfectly efficient, so the electrical demand is the converted figure divided by the efficiency, and sizing a supply from the shaft rating alone will leave the circuit short. For anything beyond rough comparison, take the running current straight from the nameplate.

Add the equipment this sizes

This result is a specification — 3.728 kW — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Mechanical horsepower is defined as 550 ft-lbf/s = 745.699872 W exactly
  • Metric horsepower (PS) differs at 735.49875 W and is not used here

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Frequently asked questions

Mechanical or metric horsepower — which does this use?
Mechanical horsepower, 745.6999 W, which is the figure used on American and British equipment. Metric horsepower (PS, CV, pk) is 735.49875 W and appears on some continental European machinery. The two differ by about 1.4%, so check which your nameplate means before relying on the result for anything tight.
Why is the motor's power draw higher than this figure?
Horsepower on a nameplate is mechanical output at the shaft. Getting that output costs more electrical input because the motor has losses. Divide the converted kilowatts by the efficiency — a 5 hp motor at 88% efficiency draws roughly 4.24 kW rather than 3.73 kW — and remember that power factor affects the current drawn on top of that.
Does starting current matter for cable sizing?
It matters a great deal. A direct-on-line induction motor can pull six to eight times its running current for the first few seconds, which drives protective device selection and voltage-drop checks even though it does not change the cable's thermal rating. Size for running current, then verify starting behaviour separately.