Loading Calculator...
Please wait a moment
Please wait a moment
Convert motor horsepower (HP) to electrical current in amperes (A) for DC, single-phase AC, and three-phase AC motors.
Typical range: 0.85-0.95 for modern motors
Typical range: 0.80-0.90 for induction motors
Where: HP = horsepower, V = voltage, Eff = motor efficiency, PF = power factor, 746 = watts per HP
| HP | 115V | 230V |
|---|---|---|
| 0.5 HP | 8 A | 4 A |
| 1 HP | 16 A | 8 A |
| 1.5 HP | 20 A | 10 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 |
| HP | 208V | 230V | 460V | 575V |
|---|---|---|---|---|
| 0.5 HP | 2.4 A | 2.2 A | 1.1 A | 0.9 A |
| 1 HP | 4.6 A | 4.2 A | 2.1 A | 1.7 A |
| 1.5 HP | 6.6 A | 6 A | 3 A | 2.4 A |
| 2 HP | 7.5 A | 6.8 A | 3.4 A | 2.7 A |
| 3 HP | 11 A | 10 A | 5 A | 4 A |
| 5 HP | 17.5 A | 15.2 A | 7.6 A | 6.1 A |
| 7.5 HP | 25.3 A | 22 A | 11 A | 9 A |
| 10 HP | 32.2 A | 28 A | 14 A | 11 A |
| 15 HP | 48.3 A | 42 A | 21 A | 17 A |
| 20 HP | 62.1 A | 54 A | 27 A | 22 A |
| 25 HP | 78.2 A | 68 A | 34 A | 27 A |
| 30 HP | 92 A | 80 A | 40 A | 32 A |
| 40 HP | 120 A | 104 A | 52 A | 41 A |
| 50 HP | 150 A | 130 A | 65 A | 52 A |
| 75 HP | 221 A | 192 A | 96 A | 77 A |
| 100 HP | 285 A | 248 A | 124 A | 99 A |
Values from NEC Table 430.250. Use nameplate FLA when available.
HP to Amps conversion is the process of determining the electrical current (in amperes) that an electric motor draws based on its horsepower rating. One mechanical horsepower equals 746 watts. However, converting HP to amps is not a simple direct conversion because the current also depends on the supply voltage, the motor's efficiency, and the power factor of the circuit. DC motors use a straightforward formula, while single-phase and three-phase AC motors require additional factors. This conversion is critical for selecting the correct wire gauge, circuit breaker size, and overload protection per the National Electrical Code (NEC). Electricians, engineers, and maintenance technicians use HP to Amps calculations daily when installing motors, sizing feeders, and designing motor control centers. NEC Tables 430.248 and 430.250 provide full-load ampere (FLA) values for standard motors that serve as the baseline for all branch circuit and feeder calculations.
Determine whether the motor is DC, single-phase AC, or three-phase AC. Check the motor nameplate for this information along with the rated HP, voltage, and full-load amps.
You need the motor HP, supply voltage, motor efficiency (typically 85–95%), and power factor (typically 0.80–0.90 for AC motors). The nameplate or manufacturer data sheet provides these values.
For DC: A = (HP × 746) ÷ (V × Eff). For single-phase AC: A = (HP × 746) ÷ (V × Eff × PF). For three-phase AC: A = (HP × 746) ÷ (√3 × V × Eff × PF).
Cross-check your calculated value against NEC Table 430.248 (single-phase) or 430.250 (three-phase). The NEC FLA values are used for sizing conductors and overcurrent protection, regardless of nameplate values.
Knowing the amp draw ensures you select conductors rated for the load, preventing overheating and fire hazards per NEC Article 430.
Circuit breakers must be sized at 125% of motor FLA for continuous duty. Accurate amp calculations prevent nuisance tripping and ensure protection.
Understanding amp draw helps identify oversized or underloaded motors, enabling energy audits and upgrades to premium-efficiency NEMA motors.
| Motor HP | FLA (230V, 3φ) | 125% FLA | Recommended Breaker | Min Wire (Cu, 75°C) |
|---|---|---|---|---|
| 1 HP | 4.2 A | 5.25 A | 15 A | 14 AWG |
| 3 HP | 10 A | 12.5 A | 15 A | 14 AWG |
| 5 HP | 15.2 A | 19 A | 20 A | 12 AWG |
| 10 HP | 28 A | 35 A | 35 A | 10 AWG |
| 20 HP | 54 A | 67.5 A | 70 A | 6 AWG |
| 50 HP | 130 A | 162.5 A | 175 A | 1/0 AWG |
| 100 HP | 248 A | 310 A | 350 A | 350 kcmil |
Values based on NEC Table 430.250 (three-phase, 230V). Always verify with local codes and the motor nameplate.
A 5 HP single-phase motor at 230V draws approximately 28 amps per NEC Table 430.248. A 5 HP three-phase motor at 230V draws approximately 15.2 amps per NEC Table 430.250. The actual nameplate FLA may differ slightly depending on the manufacturer and efficiency class.
The nameplate shows the actual measured full-load current for that specific motor. Calculated values use assumed efficiency and power factor, which vary by manufacturer and motor design. NEC requires using table values (not nameplate) for sizing branch circuit conductors and overcurrent protection devices.
Undersized conductors overheat under load, degrading insulation over time and creating a serious fire hazard. This is a code violation per NEC Article 430. Conductors must be sized at a minimum of 125% of the motor FLA to handle continuous operation and starting surges safely.
Motor starting current (locked-rotor amps) can be 5 to 8 times the full-load amps. NEC Article 430.52 allows circuit breakers to be sized larger than normal to accommodate this inrush—up to 250% of FLA for inverse-time breakers. This prevents nuisance tripping during motor startup while still providing fault protection.
VFDs change the effective frequency and voltage supplied to the motor, so the amp draw varies with speed and load. For VFD input sizing, use the drive's rated input current rather than the motor HP conversion. The output current to the motor follows standard HP to Amps relationships at the operating frequency and voltage.