Horsepower to Amps Calculator
Enter motor horsepower, voltage, phase, power factor and efficiency to calculate full-load amps (FLA) instantly. Results follow the NEC motor-sizing formula.
How do you convert HP to amps for a motor?
Multiply horsepower by 746 (watts per HP), then divide by the product of voltage, power factor and efficiency. For a 5 HP single-phase motor at 230 V, PF 0.85, η 0.90: A = (5 × 746) ÷ (230 × 0.85 × 0.90) = 3730 ÷ 175.95 = 21.2 A.
This formula is consistent with NEC Article 430. NEC Tables 430.248 and 430.250 provide standardised full-load amps for common voltage/HP ratings and are the values legally required for conductor and breaker sizing; use this calculator for quick estimates and always cross-check with the applicable NEC table and motor nameplate.
HP to Amps Reference Table (Typical Motor FLA)
| Motor HP | Single-phase 120 V | Single-phase 230 V | Three-phase 230 V | Three-phase 460 V |
|---|---|---|---|---|
| 1 HP | 9.8 A | 5.1 A | 3.4 A | 1.7 A |
| 2 HP | 19.5 A | 10.2 A | 6.8 A | 3.4 A |
| 5 HP | — | 25.4 A | 16.9 A | 8.5 A |
| 10 HP | — | 50.9 A | 33.9 A | 17.0 A |
| 25 HP | — | — | 84.7 A | 42.4 A |
| 50 HP | — | — | 169.5 A | 84.7 A |
Calculated at PF 0.85, efficiency 0.90. Always verify against the motor nameplate and NEC Tables 430.248/430.250.
Formula
Three-phase: A = (HP × 746) ÷ (√3 × V × PF × η)
DC: A = (HP × 746) ÷ (V × η)
Where: HP = rated horsepower, V = supply voltage in volts, PF = power factor (0–1), η (eta) = motor efficiency (0–1), √3 ≈ 1.7321 for three-phase systems.
Frequently Asked Questions
Use the formula A = (HP × 746) ÷ (V × PF × η). For example, a 5 HP motor at 230 V, PF 0.85, efficiency 90 % draws approximately 21.2 A.
For three-phase AC use: A = (HP × 746) ÷ (√3 × V × PF × η). The √3 ≈ 1.7321 factor accounts for the three-phase supply. A 10 HP motor at 460 V, PF 0.85, efficiency 90 % draws about 12.2 A.
NEC Tables 430.248 and 430.250 give standardised FLA values for conductor and breaker sizing per NFPA 70. They may differ from the formula because they represent typical motor characteristics rather than specific nameplate values.
Standard induction motors typically have PF 0.80–0.90 and efficiency 85–95 % at rated load. If the nameplate is unavailable, PF 0.85 and efficiency 90 % are conservative defaults commonly used in load-estimating.
A 1 HP single-phase 230 V motor at PF 0.85, efficiency 85 % draws about 4.5 A. At 120 V the same motor draws roughly 8.6 A. Always check the motor nameplate for the actual full-load current rating.