HP to kW Calculator for 3-Phase Motors
A motor nameplate HP is mechanical output. This works out what the motor actually draws electrically, including efficiency, power factor and full-load current.
Multiplying motor horsepower by 0.7457 gives the shaft output — the mechanical work the motor delivers. It does not give what the motor draws from the supply, and for anyone sizing a cable, breaker or electricity budget that distinction is the whole point.
Why Plain HP × 0.7457 Is Not Enough
A motor is not perfectly efficient. Copper losses in the windings, iron losses in the core, friction and the cooling fan all consume power that never reaches the shaft. The nameplate horsepower is what comes out; the supply must provide more than that.
There is a second layer. Induction motors draw current that lags the voltage, so the supply also carries reactive power that does no useful work. That is what power factor describes, and it determines the apparent power in kVA — the figure that actually sizes transformers, cables and switchgear.
The √3 factor — about 1.732 — appears because three-phase power is delivered across three conductors with line-to-line voltage. Omitting it underestimates three-phase power substantially, and it is the single most common mistake in motor calculations.
Standard Motor Sizes
Typical values for standard-efficiency industrial induction motors at 400 V, 0.86 power factor. Premium IE3 and IE4 motors run a few points higher on efficiency.
| HP | Shaft kW | Efficiency | Input kW | kVA | Amps @ 400 V |
|---|---|---|---|---|---|
| 1 | 0.75 | 80% | 0.93 | 1.08 | 1.6 |
| 3 | 2.24 | 87% | 2.57 | 2.99 | 4.3 |
| 5 | 3.73 | 90% | 4.14 | 4.82 | 7.0 |
| 10 | 7.46 | 91% | 8.19 | 9.53 | 13.8 |
| 25 | 18.64 | 93% | 20.05 | 23.31 | 33.6 |
| 50 | 37.28 | 94% | 39.66 | 46.12 | 66.6 |
| 100 | 74.57 | 95% | 78.49 | 91.27 | 131.7 |
Starting Current Is a Different Problem
Everything above describes steady running. A direct-on-line induction motor draws six to eight times full-load current while starting, for a few seconds. That inrush does not change your energy bill meaningfully, but it absolutely governs breaker selection, contactor rating and cable voltage drop.
If starting current is a constraint, a star-delta starter, soft starter or variable-frequency drive will reduce it. Sizing protection from full-load current alone is how nuisance tripping starts.
Power Factor and Your Bill
Poor power factor does not increase the kWh you consume, but many commercial tariffs penalise it because the supply network still has to carry the reactive current. Lightly loaded motors have notably worse power factor than fully loaded ones, which is another reason oversizing a motor costs money in ways that are easy to miss.
For the electrical side in reverse, our electric motor HP calculator works out horsepower from measured volts and amps, and HP to amps handles current directly. For running-cost budgeting over time, use HP to kWh.
Frequently Asked Questions
Multiply HP by 0.7457 for shaft kW, then divide by efficiency for electrical input. A 10 HP motor at 91% gives 7.46 kW shaft and draws about 8.19 kW.
It is √3, and it appears because three-phase power uses line-to-line voltage across three conductors. Omitting it substantially underestimates the power carried.
About 13.8 A at 400 V with 91% efficiency and 0.86 power factor. At 230 V the same motor draws roughly 24 A.
kW is real power doing useful work; kVA is apparent power including the reactive component. Cables and switchgear are sized on kVA.
Yes. Efficiency peaks near three-quarters load and falls sharply at light loads. An oversized motor runs less efficiently and at worse power factor.
Most industrial induction motors run 0.8 to 0.9 at full load, dropping considerably at partial load.
Not alone. A direct-on-line motor draws six to eight times full-load current while starting. Protection must tolerate that inrush.