What this converter does
This converter estimates a motor’s horsepower from its measured line current, for single-phase and three-phase supplies. Enter the voltage, power factor and efficiency, pick the phase, and read the HP — or swap to go from horsepower back to amps. It updates as you type.
The current delivers electrical watts; multiplying by efficiency gives mechanical output, then dividing by 746 gives HP. Results are estimates — nameplate data is authoritative. For power in kilowatts, see the Amps to kW converter.
The units it covers
Estimated horsepower depends on four inputs beyond the current — phase, voltage, power factor and efficiency.
View all units & their values
| Unit | Symbol | Value | Mainly used |
|---|---|---|---|
| Full-load current | A | I | Line current the motor draws |
| Motor power | hp | P | Mechanical output at the shaft |
| Voltage | V | V | Line-to-line for three-phase |
| Efficiency | η | eta | Output ÷ input, typically 0.85–0.95 |
The formula
Turn current into electrical watts, apply efficiency, then divide by 746:
HP = √3 × V × A × PF × η ÷ 746 — drop √3 for single-phaseWhere:
- A = measured line current
- V = supply voltage (line-to-line for 3-phase)
- PF = power factor, 0 to 1
- η = motor efficiency, 0 to 1
Worked example
A three-phase motor draws 14 A at 400 V, 0.85 PF, 0.9 efficiency. Estimate the HP.
HP = √3 × V × A × PF × η ÷ 7461.732 × 400 × 14 × 0.85 × 0.9 ÷ 746 = 9.94 hpAbout 10 HP — consistent with a 10 HP motor drawing roughly 14 A.
The units in this example
The line current a motor draws at rated load. Combined with voltage, power factor and efficiency, it estimates the mechanical horsepower.
- HP = V × A × PF × η ÷ 746 — 1ph
- HP = √3 × V × A × PF × η ÷ 746 — 3ph
- 1 A, 400 V, 3ph, 0.85 PF, 0.9 η = 0.71 hp
- √3 = 1.732
The mechanical output estimated from current. It is the electrical input times efficiency, divided by 746 watts per horsepower.
- 1 hp = 745.7 W output
- input W = HP × 746 ÷ η
- 1 hp ≈ 0.746 kW
- higher η → more HP for same amps