HP to Amps Calculator
Convert horsepower to amps for DC, single-phase and three-phase motors, using voltage, efficiency and power factor. Estimate motor current for wiring and breakers.
CURRENT
20.32 A
WATTS
3,730 W
FORMULA
I=(HP×746)/(V×Eff×PF)
HP to Amps — Reference (240V, PF=0.85, Eff=90%)
| HP | kW | Amps (1Φ) | Amps (3Φ) |
|---|---|---|---|
| 0.5 HP | 0.37 | 2.03 A | 1.17 A |
| 1 HP | 0.75 | 4.06 A | 2.35 A |
| 1.5 HP | 1.12 | 6.09 A | 3.52 A |
| 2 HP | 1.49 | 8.13 A | 4.69 A |
| 3 HP | 2.24 | 12.19 A | 7.04 A |
| 5 HP | 3.73 | 20.32 A | 11.73 A |
| 7.5 HP | 5.6 | 30.47 A | 17.59 A |
| 10 HP | 7.46 | 40.63 A | 23.46 A |
| 15 HP | 11.19 | 60.95 A | 35.19 A |
| 20 HP | 14.92 | 81.26 A | 46.92 A |
| 25 HP | 18.65 | 101.58 A | 58.65 A |
| 30 HP | 22.38 | 121.9 A | 70.38 A |
| 50 HP | 37.3 | 203.16 A | 117.29 A |
💡 How to Convert HP to Amps
To convert horsepower to amps, multiply the HP by 746 to get watts, then divide by voltage × efficiency × power factor (and also by √3 for three-phase). The result is the current a motor draws when delivering its rated horsepower.
HP to amps formulas
Single-phase AC: I = HP × 746 ÷ (V × Eff × PF)
Three-phase AC: I = HP × 746 ÷ (V × Eff × PF × √3)
Eff = motor efficiency (0–1), PF = power factor (0–1), V = line-to-line voltage for three-phase
Worked examples
- 5 HP single-phase at 240 V (Eff 0.9, PF 0.85): 5 × 746 ÷ (240 × 0.9 × 0.85) = 20.3 A.
- 10 HP three-phase at 480 V (Eff 0.9, PF 0.85): 7,460 ÷ (480 × 0.9 × 0.85 × 1.732) = 11.7 A.
- 1 HP DC motor at 90 V (Eff 0.8): 746 ÷ (90 × 0.8) = 10.4 A.
HP to amps table
Calculated at efficiency 0.9 and power factor 0.85.
| HP | 120 V 1φ | 240 V 1φ | 208 V 3φ | 400 V 3φ | 480 V 3φ |
|---|---|---|---|---|---|
| 0.5 | 4.1 | 2 | 1.4 | 0.7 | 0.6 |
| 1 | 8.1 | 4.1 | 2.7 | 1.4 | 1.2 |
| 2 | 16.3 | 8.1 | 5.4 | 2.8 | 2.3 |
| 3 | 24.4 | 12.2 | 8.1 | 4.2 | 3.5 |
| 5 | 40.6 | 20.3 | 13.5 | 7 | 5.9 |
| 7.5 | 60.9 | 30.5 | 20.3 | 10.6 | 8.8 |
| 10 | 81.3 | 40.6 | 27.1 | 14.1 | 11.7 |
| 15 | 121.9 | 60.9 | 40.6 | 21.1 | 17.6 |
| 20 | 162.5 | 81.3 | 54.1 | 28.2 | 23.5 |
| 25 | 203.2 | 101.6 | 67.7 | 35.2 | 29.3 |
| 50 | 406.3 | 203.2 | 135.3 | 70.4 | 58.6 |
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.
Formula versus NEC full-load current tables
For wire, breaker and overload sizing in the US, the National Electrical Code requires the full-load current (FLC) from its tables (Table 430.248 for single-phase and Table 430.250 for three-phase motors), not the value from a formula or the nameplate. The tables are deliberately conservative. For example, NEC Table 430.248 lists 28 A for a 5 HP, 230 V single-phase motor, and Table 430.250 lists 14 A for a 10 HP, 460 V three-phase motor, both somewhat higher than the formula gives with typical efficiency and power factor. Use the formula to understand and estimate; use the tables (and a qualified electrician) for installation.
Starting current
A motor started directly across the line draws a large inrush, commonly about 6–8 times its full-load current, for a few seconds. This matters when sizing generators, UPS units and protective devices. Soft starters and variable-frequency drives reduce the inrush.
Related conversions: amps to HP · HP to kVA · kW to amps