HP to Amps Calculator

Convert electric motor output from Horsepower (HP) or Kilowatts (kW) into full-load electrical current (Amperes) across Single-Phase, 3-Phase, and DC systems with NEC circuit breaker, wire gauge, and generator sizing.

Popular Motor Presets:
Motor Parameters Real-time Calculation
Nameplate Output
Quick:

Standard induction motors operate between 0.80 and 0.90. (DC motors use 1.0).

%

Standard motors: 80%–88%. NEMA Premium / IE3 motors: 90%–96%.

Calculation Result 3-Phase (Line-Line)
Calculated Full-Load Current:
11.7 Amps
= 8.29 kW Total Electrical Input Power
Full-Load Current (FLA): 11.7 Amps
Mechanical Output: 10 HP (7,457 W)
Active Real Power (P): 8.29 kW
Apparent Power (S): 9.75 kVA
Reactive Power (Q): 5.14 kVAR
Starting Inrush (LRA ~6x): ~70.2 Amps
NEC Breaker Sizing (125%): 20A Breaker
Copper Conductor Gauge: #14 AWG THHN Cu
Recommended Generator: 19 kW / 23.8 kVA
Live Formula:
Amps = (10 HP × 745.7) ÷ (1.732 × 480V × 0.85 × 0.90) = 11.7 Amps

How to Calculate Motor Amps from Horsepower (Formulas)

Electric motors convert electrical energy into mechanical shaft power. Because 1 mechanical Horsepower equals approximately 745.7 Watts (0.746 kW), converting output Horsepower into electrical current in Amperes requires factoring in system Voltage (V), Motor Efficiency (η), and AC Power Factor (PF / cos φ).

1-Phase AC Formula
I = (HP × 745.7) ÷ (V × PF × η)

Used for standard 120V, 208V, and 240V residential and light commercial single-phase motors.

3-Phase (Line-to-Line)
I = (HP × 745.7) ÷ (√3 × V_LL × PF × η)

Standard for industrial 208V, 240V, 480V, and 600V 3-phase delta and wye induction motors (√3 ≈ 1.732).

Direct Current (DC)
I = (HP × 745.7) ÷ (V × η)

Applies to 12V, 24V, 48V, and high-voltage DC motors with unity power factor (PF = 1.0).

NEC Motor Full-Load Amps (FLA) Quick Reference Table

Standard nominal full-load currents for typical squirrel-cage induction motors per National Electrical Code (NEC Tables 430.248 & 430.250):

Motor HP 115V (1-Phase) 230V (1-Phase) 208V (3-Phase) 230V (3-Phase) 460V (3-Phase) 575V (3-Phase)
1/2 HP 9.8 A 4.9 A 2.4 A 2.2 A 1.1 A 0.9 A
1 HP 16.0 A 8.0 A 4.6 A 4.2 A 2.1 A 1.7 A
2 HP 24.0 A 12.0 A 7.5 A 6.8 A 3.4 A 2.7 A
3 HP 34.0 A 17.0 A 10.6 A 9.6 A 4.8 A 3.9 A
5 HP 56.0 A 28.0 A 16.7 A 15.2 A 7.6 A 6.1 A
10 HP 100.0 A 50.0 A 30.8 A 28.0 A 14.0 A 11.0 A
25 HP -- -- 74.8 A 68.0 A 34.0 A 27.0 A
50 HP -- -- 143.0 A 130.0 A 65.0 A 52.0 A
100 HP -- -- 273.0 A 248.0 A 124.0 A 99.0 A

Frequently Asked Questions (FAQ)

What is the difference between Full-Load Amps (FLA) and Locked-Rotor Amps (LRA)?

FLA (Full-Load Amps) is the steady-state current drawn when the motor is delivering its rated horsepower output. LRA (Locked-Rotor Amps) is the momentary startup inrush current drawn when voltage is first applied to a stationary rotor, typically 500% to 600% of FLA.

Why do conductors require 125% ampacity sizing for electric motors?

Under NEC Article 430.22, motor branch circuit conductors must have an ampacity rating not less than 125% of the motor full-load current to prevent conductor overheating under continuous maximum load duty cycles.

How do I calculate generator size to start an electric motor?

To prevent voltage drop that causes stalling or breaker tripping, multiply the electric motor’s running active kilowatt rating (kW = HP × 0.746 ÷ Efficiency) by 2.0x to 3.0x for standard direct-on-line (DOL) starts, or 1.5x to 2.0x for soft-starter systems.