Amps to HP Calculator
Convert amps to horsepower (HP) for DC, single-phase and three-phase motors using voltage, power factor and efficiency. Estimate a motor's output from its current.
HORSEPOWER
4.92 HP
WATTS
4,080 W
FORMULA
HP=(I×V×PF×Eff)/746
1 HP
= 746 watts
💡 How to Convert Amps to HP
To convert amps to horsepower, multiply current × voltage (× power factor for AC, × √3 for three-phase) to get input watts, multiply by motor efficiency to get output watts, then divide by 746. The answer is the mechanical horsepower the motor delivers at that current.
Amps to HP formulas
Single-phase AC: HP = I × V × PF × Eff ÷ 746
Three-phase AC: HP = I × V × PF × Eff × √3 ÷ 746
Worked examples
- 20 A at 240 V single-phase (PF 0.85, Eff 0.9): 20 × 240 × 0.85 × 0.9 ÷ 746 = 4.92 HP.
- 40 A at 480 V three-phase (PF 0.85, Eff 0.9): 40 × 480 × 0.85 × 0.9 × 1.732 ÷ 746 = 34.1 HP.
- 50 A at 48 V DC (Eff 0.85), such as a golf-cart motor: 50 × 48 × 0.85 ÷ 746 = 2.73 HP.
Amps to HP table
Calculated at power factor 0.85 and efficiency 0.9.
| Amps | 120 V 1φ | 240 V 1φ | 208 V 3φ | 400 V 3φ | 480 V 3φ |
|---|---|---|---|---|---|
| 5 | 0.62 | 1.23 | 1.85 | 3.55 | 4.26 |
| 10 | 1.23 | 2.46 | 3.69 | 7.1 | 8.53 |
| 15 | 1.85 | 3.69 | 5.54 | 10.66 | 12.79 |
| 20 | 2.46 | 4.92 | 7.39 | 14.21 | 17.05 |
| 30 | 3.69 | 7.38 | 11.08 | 21.31 | 25.58 |
| 40 | 4.92 | 9.84 | 14.78 | 28.42 | 34.1 |
| 50 | 6.15 | 12.31 | 18.47 | 35.52 | 42.63 |
| 75 | 9.23 | 18.46 | 27.71 | 53.28 | 63.94 |
| 100 | 12.31 | 24.61 | 36.94 | 71.05 | 85.26 |
Which horsepower?
These calculators use 1 HP = 746 W, the standard mechanical (imperial) horsepower (more precisely 745.7 W). Metric horsepower (PS or CV), used on some European and Asian equipment, is 735.5 W. Motor nameplate horsepower is the output at the shaft; the electrical power drawn is higher because of motor losses, which is why efficiency appears in the formulas.
Typical values: small single-phase motors often run at 70–85% efficiency and a power factor of 0.7–0.85; larger three-phase premium-efficiency motors exceed 90% efficiency with power factors around 0.85–0.9 at full load. Both efficiency and power factor drop when a motor is lightly loaded. The nameplate is the best source.
Using measured current
If you measure a motor's running current with a clamp meter, the result tells you roughly how hard it is working. A motor drawing well below its nameplate amps is lightly loaded, which also means lower efficiency and power factor than the nameplate values, so the calculated horsepower will be an estimate.
Related conversions: HP to amps · amps to kW · kVA to HP