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kW / HP / Amps Converter

I = P / (√3 × V × PF × η) [three-phase motor case] kW, HP, W, A, V

For motors, this converts shaft power. "kW" and "HP" on a motor nameplate normally mean mechanical output; the electrical input is higher because of losses (efficiency). For resistive loads (heaters, incandescent), input power equals output — set efficiency to 1 and power factor to 1.

Convert between kW, HP, watts, and amps

Four conversions in one tool. Pick what you want to convert, choose the direction (e.g. kW → HP or HP → kW), and enter the input value. For anything involving amps you’ll also enter voltage, phase, and load type — because amps depend on how the power is being used.

The load-type dropdown does the heavy lifting

Power factor and efficiency confuse people who just want a quick answer. The Load type selector fills sensible defaults so beginners don’t have to know what “cos φ” means, and lets pros override them:

  • Resistive (heater, incandescent, DC) — power factor 1, no efficiency losses. This is the case for baseboard heaters, electric water heaters, incandescent bulbs, and any pure resistance load. Both PF and η fields hide because they’re not applicable.
  • Motor (induction, typical) — defaults to PF 0.85 and efficiency 0.90. The kW/HP figure is treated as mechanical shaft power, and efficiency converts to electrical input for the amps calculation.
  • AC load, generic — defaults to PF 0.85 with no efficiency correction (treats the kW/HP as electrical input directly). Use this for compressors, VFDs, LED lighting drivers — anything AC where you know the electrical draw already.
  • DC circuit — no phase, no power factor. Just V × I = P.

The formulas

kW ↔ HP (mechanical): 1 HP = 745.7 W = 0.7457 kW. Multiply or divide.

kW ↔ metric HP (PS / CV): 1 metric HP = 735.5 W = 0.7355 kW. Slightly smaller than mechanical HP; common on European automotive and small-motor spec sheets.

Amps calculations:

  • DC or resistive: I = P / V
  • Single-phase AC: I = P / (V × PF)
  • Three-phase AC: I = P / (√3 × V × PF)
  • For motors, divide by efficiency too, since nameplate kW/HP is shaft power: I = Pshaft / (Vfactor × PF × η)

Mechanical HP vs metric HP — which one to pick?

Two definitions of “horsepower” exist and they’re close but not identical:

  • Mechanical HP (also “imperial HP” or “hp(I)”) = 745.7 W. Used in the US, on most industrial motors, air compressors, and North American automotive.
  • Metric HP (also “PS” in German, “CV” in French/Italian/Spanish, “ch” in French, “pk” in Dutch) = 735.5 W. Common on European car spec sheets and some small European motors.

The difference is about 1.4%. For most applications it doesn’t matter, but if you’re translating a European car’s “150 PS” figure to “148 HP” you’re doing the mechanical-HP conversion correctly.

Common conversions worth remembering

  • 1 kW ≈ 1.34 HP
  • 1 HP ≈ 0.75 kW (rounded up for quick mental math)
  • 1 kW at 230 V single-phase resistive ≈ 4.35 A
  • 1 kW at 400 V three-phase, PF=0.85 ≈ 1.70 A
  • Common motor rule of thumb: kW × 2 ≈ FLA at 400 V three-phase (rough — real values from formula)

Important limitations

This converter treats input power for motors as shaft power (mechanical output) — matching the convention on IEC/NEMA motor nameplates. For a motor spec sheet listing “input power” instead, use the “AC load, generic” preset to skip the efficiency correction. This tool doesn’t apply:

  • Voltage regulation or line drop over the run
  • Starting current — see the Motor Starting Current calculator for that
  • NEC 125% continuous-load derating for wire sizing — see the Motor FLA calculator

For code-compliant motor circuit design, cross-reference the Motor FLA & VFD Sizing calculator and applicable code (NEC Article 430 in the US, IEC 60364 / BS 7671 in Europe).

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