Horsepower to Amps Calculator

Q: How many amps does a 1 HP motor draw?

A 1 HP single-phase motor at 120V draws about 8.6 A of running current at 85% efficiency and PF 0.85 (this is what the meter reads). For NEC branch-circuit sizing, the value you must use is the 16 A full-load current from NEC Table 430.248 (the 115V column covers 110-120V per 430.6(A)(1)). At 230V the table FLC drops to 8 A. These are different numbers used for different purposes and both show up on every result page.

Convert single-phase and three-phase AC motor horsepower to both the calculated running current (what the meter reads at full load) and the NEC Table 430.248 / 430.250 full-load current (what Article 430 requires for branch-circuit conductor, switch, and OCP sizing). Use the running amps for metering and energy cost. Use the table FLC for breaker and wire sizing under NEC 430.6(A)(1). DC motors are shown for reference only, NEC 430.6(A)(3) requires using the motor nameplate with Table 430.247 for DC branch-circuit sizing, so use the nameplate and a licensed electrician for actual DC installations.

Horsepower (HP)

Motor Type

Voltage (Volts)

Motor Efficiency

Power Factor

= 8.6 amps running (meter)

16 amps NEC Table 430.248 FLC (code sizing)

Running: (1 × 746) ÷ (120 × 0.85 × 0.85) = 8.6 A · NEC 430.248 FLC: 16 A

See full breakdown for 1 HP at 120V

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What Is HP to Amps?

Horsepower (HP) measures mechanical output. Amps measure electrical current. Every motor is rated in HP, but every circuit breaker and wire is rated in amps. This conversion bridges the gap. One HP equals 746 watts, but a motor rated at 1 HP draws more than 746W of electrical power because no motor is 100% efficient.

The Formula

Amps = (HP × 746) ÷ (Volts × Efficiency × Power Factor)

Efficiency and power factor both reduce the effective output. A motor with 85% efficiency wastes 15% as heat. A power factor of 0.85 means the motor draws reactive current that does no mechanical work. Both increase the amp draw above what a simple watts-to-amps conversion would predict.

NEC Reference Values for Motor Branch Circuits

Final conductor, breaker, disconnect, and overload selection is an install decision your electrician makes against the motor nameplate, the actual install conditions, and any 430/440 provisions. The percentages and section references below are NEC reference values for context, not prescriptive install picks. Motor branch circuits follow Article 430 of the NEC, which uses a different sizing base than general branch circuits. Three things to know:

Sizing base (NEC 430.6(A)(1)): Branch-circuit conductors, switches, and overcurrent devices are sized from the full-load current in NEC Table 430.248 (single-phase) or 430.250 (three-phase), not from the motor nameplate and not from a calculated watts-based current. The calculator above surfaces both numbers so you can see them side by side.
Branch-circuit conductor (NEC 430.22): Conductor ampacity must be at least 125% of the table FLC. Motor branch-circuit conductors are exempt from the 240.4(D) small-conductor rule via 240.4(G), so a 10 AWG Cu conductor can legally sit on a 30A motor branch even though the general-branch cap is also 30A.
Branch-circuit OCP (NEC Table 430.52(C)(1)): NEC Table 430.52(C)(1) lists branch-circuit short-circuit / ground-fault protection percentages by device type: inverse-time circuit breaker up to 250% of table FLC, dual-element (time-delay) fuse up to 175%, non-time-delay fuse up to 300%, instantaneous-trip breaker up to 800%. These percentages are reference caps, not defaults. Pick the device type first, then apply the matching percentage. NEC 430.52(C)(1)(a) permits rounding up to the next standard size if the motor will not start at the calculated value.
Startup (LRA): Squirrel-cage induction motors draw roughly 5-7× the table FLC for 2-5 seconds at startup. The elevated OCP percentages above are what let the breaker ride through that inrush without tripping. The exact LRA comes from the motor's NEMA code letter.
Voltage matters: A 1 HP single-phase motor has a table FLC of 16 A at 115V but only 8 A at 230V. Higher voltage means lower current and smaller wire for the same mechanical output.

Single-Phase Running Current

Calculated single-phase running current at 85% efficiency and PF 0.85, what the meter reads at full load on a single-phase circuit. These are not the values to use for NEC branch-circuit sizing; use the NEC Table 430.248 values further down for that.

HP	120V 1Φ	230V 1Φ	240V 1Φ
1/4 HP	2.15A	1.12A	1.08A
1/2 HP	4.3A	2.24A	2.15A
3/4 HP	6.45A	3.37A	3.23A
1 HP	8.6A	4.49A	4.3A
1.5 HP	12.91A	6.73A	6.45A
2 HP	17.21A	8.98A	8.6A
3 HP	25.81A	13.47A	12.91A
5 HP	43.02A	22.45A	21.51A
7.5 HP	64.53A	33.67A	32.27A
10 HP	86.04A	44.89A	43.02A

Three-Phase Running Current

Calculated three-phase running current per line at 85% efficiency and PF 0.85, using I = (HP × 746) ÷ (√3 × V_LL × Eff × PF). Links open the result page in three-phase mode. 208V, 230V, and 240V are common commercial three-phase values; 480V is common US industrial three-phase.

HP	208V 3Φ	230V 3Φ	240V 3Φ	480V 3Φ
1/4 HP	0.7165A	0.648A	0.621A	0.3105A
1/2 HP	1.43A	1.3A	1.24A	0.621A
3/4 HP	2.15A	1.94A	1.86A	0.9315A
1 HP	2.87A	2.59A	2.48A	1.24A
1.5 HP	4.3A	3.89A	3.73A	1.86A
2 HP	5.73A	5.18A	4.97A	2.48A
3 HP	8.6A	7.78A	7.45A	3.73A
5 HP	14.33A	12.96A	12.42A	6.21A
7.5 HP	21.5A	19.44A	18.63A	9.31A
10 HP	28.66A	25.92A	24.84A	12.42A

NEC Table 430.248 FLC, Single-Phase (Code Sizing)

Full-load current values from NEC Table 430.248 used for branch-circuit conductor, switch, and overcurrent protection sizing under NEC 430.6(A)(1). The 115V column covers 110-120V systems; the 230V column covers 220-240V. Dashes mark HP / voltage combinations not listed in the table.

HP	115V (110-120V)	200V	208V	230V (220-240V)
1/6 HP	4.4 A	2.5 A	2.4 A	2.2 A
1/4 HP	5.8 A	3.3 A	3.2 A	2.9 A
1/3 HP	7.2 A	4.1 A	4 A	3.6 A
1/2 HP	9.8 A	5.6 A	5.4 A	4.9 A
3/4 HP	13.8 A	7.9 A	7.6 A	6.9 A
1 HP	16 A	9.2 A	8.8 A	8 A
1.5 HP	20 A	11.5 A	11 A	10 A
2 HP	24 A	13.8 A	13.2 A	12 A
3 HP	34 A	19.6 A	18.7 A	17 A
5 HP	56 A	32.2 A	30.8 A	28 A
7.5 HP	80 A	46 A	44 A	40 A
10 HP	100 A	57.5 A	55 A	50 A

NEC Table 430.250 FLC, Three-Phase (Code Sizing)

Full-load current values from NEC Table 430.250 (three-phase squirrel-cage / synchronous motors) used for branch-circuit conductor, switch, and overcurrent protection sizing under NEC 430.6(A)(1). The 230V column covers 220-240V; the 460V column covers 440-480V.

HP	200V	208V	230V (220-240V)	460V (440-480V)	575V
1/2 HP	2.5 A	2.4 A	2.2 A	1.1 A	0.9 A
3/4 HP	3.7 A	3.5 A	3.2 A	1.6 A	1.3 A
1 HP	4.8 A	4.6 A	4.2 A	2.1 A	1.7 A
1.5 HP	6.9 A	6.6 A	6 A	3 A	2.4 A
2 HP	7.8 A	7.5 A	6.8 A	3.4 A	2.7 A
3 HP	11 A	10.6 A	9.6 A	4.8 A	3.9 A
5 HP	17.5 A	16.7 A	15.2 A	7.6 A	6.1 A
7.5 HP	25.3 A	24.2 A	22 A	11 A	9 A
10 HP	32.2 A	30.8 A	28 A	14 A	11 A
15 HP	48.3 A	46.2 A	42 A	21 A	17 A
20 HP	62.1 A	59.4 A	54 A	27 A	22 A
25 HP	78.2 A	74.8 A	68 A	34 A	27 A
30 HP	92 A	88 A	80 A	40 A	32 A
40 HP	120 A	114 A	104 A	52 A	41 A
50 HP	150 A	143 A	130 A	65 A	52 A
75 HP	221 A	211 A	192 A	96 A	77 A
100 HP	285 A	273 A	248 A	124 A	99 A

DC motors are not listed in this calculator. NEC 430.6(A)(3) requires using the motor nameplate full-load current with NEC Table 430.247 for DC branch-circuit sizing, so there is no general-purpose DC lookup that matches how the code actually works.

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Frequently Asked Questions

How do I convert horsepower to amps?expand_more

For the running current you will see on a meter, use Amps = (HP × 746) ÷ (Volts × Efficiency × Power Factor). One HP equals 746 watts of mechanical output; efficiency (typically 80-90%) and power factor (typically 0.80-0.85) both raise the electrical draw above that figure. For NEC branch-circuit conductor, switch, and OCP sizing, you should not use that calculated value. Per NEC 430.6(A)(1), motor branch circuits are sized from the full-load current in Table 430.248 (single-phase) or Table 430.250 (three-phase), which already incorporates typical efficiency and power factor.

How many amps does a 1 HP motor draw?expand_more

A 1 HP single-phase motor at 120V draws about 8.6 A of running current at 85% efficiency and PF 0.85 (this is what the meter reads). For NEC branch-circuit sizing, the value you must use is the 16 A full-load current from NEC Table 430.248 (the 115V column covers 110-120V per 430.6(A)(1)). At 230V the table FLC drops to 8 A. These are different numbers used for different purposes and both show up on every result page.

What is motor efficiency?expand_more

Motor efficiency is the percentage of electrical power converted to mechanical power. A motor with 85% efficiency wastes 15% as heat, so a 1 HP motor with 746 W of mechanical output draws about 746 ÷ 0.85 = 878 W of electrical input at the terminals. Higher efficiency means lower running amps and lower electrical input for the same horsepower.

Why do motors draw more amps at startup?expand_more

Squirrel-cage induction motors draw 5-7 times the NEC table full-load current for 2-5 seconds during startup (locked-rotor amps, or LRA). The exact multiplier is set by the NEMA code letter on the motor nameplate. This is why NEC 430.52(C)(1) allows motor branch-circuit OCP to be rated well above the running current. The percentage depends on the device type: inverse-time circuit breakers may go up to 250% of the table FLC, dual-element fuses up to 175%, instantaneous-trip breakers up to 800%, and non-time-delay fuses up to 300%. These are ceilings, not defaults.

What about fractional horsepower motors?expand_more

Small motors (1/6 HP to 3/4 HP) are common in fans, pumps, furnace blowers, and power tools. A 1/2 HP single-phase motor at 120V has a calculated running current around 4-5 A but a NEC Table 430.248 FLC of 9.8 A, which is the number used for branch-circuit conductor and OCP sizing. Even though the motor draws less running current than a typical 15A household branch, sizing and overcurrent rules in Article 430 still apply.

This calculator provides estimates for reference purposes only. Always consult a licensed electrician and verify compliance with the National Electrical Code (NEC) and local electrical codes before performing any electrical work.

Standards & References

This page cites the following electrical codes and standards. Always consult the current edition of your local adopted standard for authoritative requirements.

NEC 430.6(A)(1). Motor full-load current values for general motor applications shall be taken from Tables 430.247 through 430.250 rather than the motor nameplate for the purposes of sizing conductors, switches, and overcurrent devices.
National Electrical Code (NFPA 70), Article 430, Motors, Motor Circuits, and Controllers. Reference →
NEC 430.52 and Table 430.52(C)(1). Motor branch-circuit short-circuit and ground-fault protection. Maximum ratings from Table 430.52(C)(1): non-time-delay fuse 300%, dual-element (time-delay) fuse 175%, instantaneous-trip breaker 800%, and inverse-time breaker 250% of full-load amps. The elevated percentages allow for motor locked-rotor startup current.
National Electrical Code (NFPA 70), Article 430, Motors, Motor Circuits, and Controllers. Reference →
NEC Table 310.16. Allowable ampacities of insulated conductors rated up to 2000V, 60°C through 90°C, not more than three current-carrying conductors in raceway or cable.
National Electrical Code (NFPA 70), Article 310, Conductors for General Wiring. Reference →
DOE 10 CFR Part 431. US Department of Energy energy conservation standards for electric motors. Sets minimum nominal full-load efficiencies for small, medium, and large electric motors sold in the US, including NEMA Premium and IE3/IE4 equivalents.
US Department of Energy. Reference →
NEMA MG 1. National standard for motors and generators. Defines motor efficiency classes, power factor values, insulation temperature ratings, service factor, and locked-rotor currents. The industry reference for motor nameplate interpretation.
National Electrical Manufacturers Association. Reference →

Disclaimer: The information on this page is provided for reference. Always consult a licensed electrician and the current edition of your local adopted electrical code before performing electrical work.