HP to Amps Calculator
Convert horsepower to amps for DC, single-phase, and three-phase motors. Enter the motor HP, voltage, efficiency, and power factor to calculate the full-load current — or flip the direction to convert amps back to horsepower.
Typical: 0.85–0.95 (default 0.90)
Typical: 0.80–0.90 (default 0.85)
Note: For sizing conductors and overcurrent protection, the NEC requires using the full-load current values from Tables 430.248 and 430.250 — not calculated or nameplate values (NEC 430.6(A)). Use this calculator for estimates and load planning.
How to Convert HP to Amps
One horsepower equals 746 watts of mechanical output.To find the electrical current a motor draws, convert HP to watts, then account for the motor's efficiency (η) and, for AC motors, the power factor (PF). Because no motor is 100% efficient, the electrical input is always greater than the mechanical output.
DC: Amps = HP × 746 ÷ (Volts × η)
Single-phase AC: Amps = HP × 746 ÷ (Volts × η × PF)
Three-phase AC: Amps = HP × 746 ÷ (1.732 × Volts × η × PF)
Worked example: a 10 HP three-phase motor on a 460V circuit with 90% efficiency and a 0.85 power factor:
Amps = 10 × 746 ÷ (1.732 × 460 × 0.90 × 0.85)
Amps = 7,460 ÷ 609.5 ≈ 12.2 A
The NEC table value for a 10 HP, 460V three-phase motor is 14 amps — higher than the calculated 12.2 A because the tables are intentionally conservative. When sizing conductors and overcurrent protection, NEC 430.6(A) requires you to use the table values below, not calculated or nameplate current.
HP to Amps Chart (NEC Full-Load Currents)
Three-phase induction motor full-load currents per NEC Table 430.250:
| Horsepower | 230V Three-Phase | 460V Three-Phase |
|---|---|---|
| 1 HP | 3.6 A | 1.8 A |
| 2 HP | 6.8 A | 3.4 A |
| 3 HP | 9.6 A | 4.8 A |
| 5 HP | 15.2 A | 7.6 A |
| 7.5 HP | 22 A | 11 A |
| 10 HP | 28 A | 14 A |
| 15 HP | 42 A | 21 A |
| 20 HP | 54 A | 27 A |
| 25 HP | 68 A | 34 A |
| 30 HP | 80 A | 40 A |
| 40 HP | 104 A | 52 A |
| 50 HP | 130 A | 65 A |
Single-phase motor full-load currents per NEC Table 430.248:
| Horsepower | 115V Single-Phase | 230V Single-Phase |
|---|---|---|
| 1 HP | 16 A | 8 A |
| 2 HP | 24 A | 12 A |
| 3 HP | 34 A | 17 A |
| 5 HP | 56 A | 28 A |
| 7.5 HP | 80 A | 40 A |
| 10 HP | 100 A | 50 A |
Important:NEC 430.6(A)(1) requires these table values — not the motor nameplate current — for sizing branch-circuit conductors, short-circuit protection, and disconnects. Nameplate current is used only for overload protection.
Frequently Asked Questions
How do you convert HP to amps?
Multiply horsepower by 746 to get watts, then divide by the voltage times efficiency times power factor. For single-phase AC: Amps = HP × 746 ÷ (Volts × Efficiency × Power Factor). For three-phase AC: Amps = HP × 746 ÷ (1.732 × Volts × Efficiency × Power Factor). For DC motors, omit the power factor: Amps = HP × 746 ÷ (Volts × Efficiency).
How many amps does a 5 HP motor draw?
Per NEC full-load current tables, a 5 HP single-phase motor draws 56 amps at 115V or 28 amps at 230V (Table 430.248). A 5 HP three-phase motor draws 15.2 amps at 230V or 7.6 amps at 460V (Table 430.250). Higher voltage and three-phase power both reduce the current for the same horsepower.
Why is 746 watts one horsepower?
One mechanical horsepower is defined as 550 foot-pounds of work per second, a standard James Watt established to compare steam engines to draft horses. Converting 550 ft-lb/s to SI units gives 745.7 watts, rounded to 746 W in electrical calculations. Because motors are not 100% efficient, the electrical input power is always higher than 746 W per HP of output.
Why do calculated amps differ from NEC table values?
The formula gives the theoretical current for the exact efficiency and power factor you enter, while NEC Tables 430.248 and 430.250 list standardized, conservative full-load currents that represent typical motors at rated speed. The table values are intentionally on the high side so that conductors and overcurrent devices sized from them are safe for virtually any motor of that horsepower and voltage.
Should I use nameplate amps or NEC table values for wire sizing?
Use the NEC table values. NEC 430.6(A)(1) requires that conductor ampacity, short-circuit protection, and disconnect ratings be based on the full-load current values in Tables 430.247 through 430.250 — not the motor nameplate. The nameplate current is used only for sizing separate overload protection per 430.6(A)(2).
How many amps does a 10 HP motor draw?
Per NEC tables, a 10 HP single-phase motor draws 100 amps at 115V or 50 amps at 230V. A 10 HP three-phase motor draws 28 amps at 230V or 14 amps at 460V. By formula at 460V three-phase with 90% efficiency and 0.85 power factor, the calculated current is about 12.2 amps — the NEC table value of 14 amps is the conservative figure used for circuit design.
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