HP to Amps Calculator
Estimate the current a motor draws from its horsepower, voltage, efficiency and power factor — for DC, single-phase and three-phase motors — and look up the NEC full-load current used for code sizing.
HP to amps formulas
Motor horsepower is mechanical output. Electrical input is larger by the efficiency η (typically 0.75–0.85 for small single-phase motors and 0.88–0.96 for three-phase industrial motors). AC motors also draw reactive current, captured by the power factor PF (about 0.7–0.9 at full load). One mechanical horsepower = 745.7 W.
Worked examples
Three-phase: 10 hp, 460 V, η = 90%, PF = 0.85: I = 7457 / (1.732 × 460 × 0.90 × 0.85) = 12.2 A. NEC Table 430.250 lists 14 A — the table is deliberately conservative.
Single-phase: 2 hp, 230 V, η = 80%, PF = 0.85: I = 1491.4 / (230 × 0.80 × 0.85) = 9.54 A (NEC Table 430.248: 12 A).
DC: 1 hp, 90 V, η = 80%: I = 745.7 / (90 × 0.80) = 10.4 A.
NEC Table 430.248 – single-phase motor full-load current (A)
| HP | 115 V | 200 V | 208 V | 230 V |
|---|---|---|---|---|
| 1/6 | 4.4 | 2.5 | 2.4 | 2.2 |
| 1/4 | 5.8 | 3.3 | 3.2 | 2.9 |
| 1/3 | 7.2 | 4.1 | 4.0 | 3.6 |
| 1/2 | 9.8 | 5.6 | 5.4 | 4.9 |
| 3/4 | 13.8 | 7.9 | 7.6 | 6.9 |
| 1 | 16 | 9.2 | 8.8 | 8.0 |
| 1-1/2 | 20 | 11.5 | 11.0 | 10 |
| 2 | 24 | 13.8 | 13.2 | 12 |
| 3 | 34 | 19.6 | 18.7 | 17 |
| 5 | 56 | 32.2 | 30.8 | 28 |
| 7-1/2 | 80 | 46.0 | 44.0 | 40 |
| 10 | 100 | 57.5 | 55.0 | 50 |
NEC Table 430.250 – three-phase induction motor full-load current (A)
| HP | 200 V | 208 V | 230 V | 460 V | 575 V |
|---|---|---|---|---|---|
| 1/2 | 2.5 | 2.4 | 2.2 | 1.1 | 0.9 |
| 3/4 | 3.7 | 3.5 | 3.2 | 1.6 | 1.3 |
| 1 | 4.8 | 4.6 | 4.2 | 2.1 | 1.7 |
| 1-1/2 | 6.9 | 6.6 | 6.0 | 3.0 | 2.4 |
| 2 | 7.8 | 7.5 | 6.8 | 3.4 | 2.7 |
| 3 | 11.0 | 10.6 | 9.6 | 4.8 | 3.9 |
| 5 | 17.5 | 16.7 | 15.2 | 7.6 | 6.1 |
| 7-1/2 | 25.3 | 24.2 | 22 | 11 | 9 |
| 10 | 32.2 | 30.8 | 28 | 14 | 11 |
| 15 | 48.3 | 46.2 | 42 | 21 | 17 |
| 20 | 62.1 | 59.4 | 54 | 27 | 22 |
| 25 | 78.2 | 74.8 | 68 | 34 | 27 |
| 30 | 92 | 88 | 80 | 40 | 32 |
| 40 | 120 | 114 | 104 | 52 | 41 |
| 50 | 150 | 143 | 130 | 65 | 52 |
| 60 | 177 | 169 | 154 | 77 | 62 |
| 75 | 221 | 211 | 192 | 96 | 77 |
| 100 | 285 | 273 | 248 | 124 | 99 |
| 125 | 359 | 343 | 312 | 156 | 125 |
| 150 | 414 | 396 | 360 | 180 | 144 |
| 200 | 552 | 528 | 480 | 240 | 192 |
Values from NFPA 70 (NEC) Tables 430.248 and 430.250, unchanged across the 2017–2023 editions. Currents are permitted for system voltages of 110–120, 220–240, 440–480 and 550–600 V. Squirrel-cage and wound-rotor induction motors at usual belted-motor speeds.
Calculated current vs. NEC table current
NEC 430.6(A)(1) requires the table full-load current, not the nameplate or a calculated value, for sizing branch-circuit conductors (125% per 430.22), short-circuit and ground-fault protection, and disconnects. The motor nameplate current is used for overload protection (430.32). Use the calculator for estimates, energy studies and non-NEC work; use the tables for code sizing.
Frequently asked questions
How many amps does a 1 hp motor draw?
From NEC Table 430.248, a 1 hp single-phase motor is 16 A at 115 V and 8 A at 230 V. A 1 hp three-phase motor is 4.2 A at 230 V and 2.1 A at 460 V (Table 430.250).
How do I convert HP to amps?
Multiply horsepower by 745.7 to get watts, divide by efficiency, then divide by voltage (DC), by voltage × power factor (single-phase), or by √3 × voltage × power factor (three-phase).
Why is the NEC table higher than my calculation?
The NEC tables are conservative values intended to cover typical motors of that rating, including lower-efficiency and lower-power-factor designs, so conductors and protection are not undersized.
What efficiency and power factor should I use?
Use the nameplate if available. Otherwise about 85–92% efficiency and 0.85 PF for three-phase motors over 5 hp, and 70–80% efficiency with 0.75–0.85 PF for small single-phase motors.
How many amps is a 10 hp 3-phase motor?
NEC Table 430.250: 30.8 A at 208 V, 28 A at 230 V, 14 A at 460 V and 11 A at 575 V.