HP to Amps Calculator
Evaluate electrical current demands in amperes from mechanical motor horsepower ratings, or convert amps back to HP. Settle phase configuration, voltage inputs, and efficiencies.
High-Precision Motor Current Tool
How to Use the HP to Amps Calculator
Converting motor output horsepower (HP) to electrical current draw in amperes is direct.
- 1Enter Horsepower: Input the mechanical output power rating in horsepower (HP).
- 2Select Phase: Select Single-Phase AC, Three-Phase AC, or DC based on system supply.
- 3Voltage: Input the operating voltage in volts (V) (e.g. 120V, 230V, or 460V).
- 4Efficiency & PF: Set motor efficiency % and power factor (for AC circuits).
How to Convert HP to Amps
In industrial plant design, mechanical power outputs are rated in horsepower (HP), while circuit breakers, overload heaters, and feeder conductors are sized by their current capacity in amperes (Amps). Converting HP to Amps requires factoring in winding conversion efficiency (to determine total input power) and circuit phase displacement (power factor) across alternating or direct currents.
Real-Life Sizing Scenarios
Scenario 1: Sizing a Three-Phase Exhaust Fan Motor
An electrical designer plans for a 10 HP ventilation fan motor running on a three-phase 460V supply. Winding nameplate specs list 88% efficiency and a 0.84 lagging power factor:
Input Watts = (10 HP × 746) ÷ 0.88 = 8,477.27 W
Current (Amps) = 8,477.27 W ÷ (√3 × 460V × 0.84) = 8,477.27 ÷ 669.26 = 12.67 Amps
Scenario 2: Sizing a DC Hydraulic Pump Motor
A backup hydraulic pump is driven by a 1 HP DC motor connected to a 12V automotive battery bank. Motor design efficiency is rated at 80%:
Current (Amps) = (1 HP × 746) ÷ (12V × 0.80) = 746 ÷ 9.6 = 77.71 Amps
Step-by-Step Manual Sizing Guide
- 1Obtain Motor HP: Check the mechanical nameplate horsepower rating (HP).
- 2Obtain System Voltage and Phase: Identify if the line is Single-Phase, Three-Phase AC, or DC, and its operating voltage.
- 3Convert Output to Input Watts: Divide mechanical output by efficiency:
Watts_in = (HP × 746) ÷ (Eff % ÷ 100). - 4Calculate Continuous Current:
- Single-Phase AC:
Amps = Watts_in ÷ (Voltage × PF) - Three-Phase AC:
Amps = Watts_in ÷ (√3 × Voltage × PF) - DC:
Amps = Watts_in ÷ Voltage
- Single-Phase AC:
HP to Amps Conversion Chart
The table below provides current draw (Amps) equivalents for standard motor sizes (Single Phase vs. Three Phase AC at 230V, 85% Efficiency, 0.90 PF):
| Motor Power (HP) | Input Power (Watts) | Single Phase Amps (230V) | Three Phase Amps (230V) |
|---|---|---|---|
| 1 HP | 878 W | 4.24 A | 2.45 A |
| 2 HP | 1,755 W | 8.48 A | 4.90 A |
| 5 HP | 4,388 W | 21.20 A | 12.24 A |
| 10 HP | 8,776 W | 42.40 A | 24.48 A |
| 20 HP | 17,553 W | 84.80 A | 48.96 A |
HP to Amps 3 Phase Formula
Determining the full-load current of a three-phase motor incorporates the phase angle multiplier (√3 ≈ 1.732) and the motor efficiency (η) rating. Sizing formula:
Amps = (HP × 746) ÷ (√3 × Voltage × PF × η)
Where HP represents the mechanical shaft output power, and the efficiency η is in decimal form (e.g. 0.85 for 85%).
1 HP to Amps 220V
Sizing the continuous current draw for a standard 1 HP single-phase motor running on a 220V power line. Sizing at 85% efficiency and a power factor of 0.85:
Amps = (1 × 746) ÷ (220 × 0.85 × 0.85) = 746 ÷ 158.95 = 4.69 Amps
10 HP to Amps 3 Phase
Sizing the electrical current drawn by a 10 HP three-phase industrial motor operating on a 460V line. Sizing at a standard 88% efficiency and a PF of 0.82:
Amps = (10 × 746) ÷ (√3 × 460 × 0.88 × 0.82) = 7460 ÷ 574.93 = 12.98 Amps
Motor HP to Amps
To convert any electric motor horsepower (HP) rating to continuous current draw in amperes (Amps), you must first check the nameplate details for phase type, efficiency, voltage, and power factor. These parameters define how much electrical energy must be supplied to generate the rated mechanical mechanical output.
3 Phase Motor HP to Amps Chart
This reference chart lists standard three-phase motor current draws at common industrial voltages (assuming a standard motor efficiency of 85% and a PF of 0.85):
| Motor Size | Amps at 208V | Amps at 230V | Amps at 460V |
|---|---|---|---|
| 1 HP | 2.87 A | 2.59 A | 1.30 A |
| 5 HP | 14.33 A | 12.96 A | 6.48 A |
| 10 HP | 28.66 A | 25.92 A | 12.96 A |
| 25 HP | 71.65 A | 64.80 A | 32.40 A |
| 50 HP | 143.30 A | 129.59 A | 64.80 A |
5 HP to Amps
Sizing the continuous amperage drawn by a 5 HP single-phase motor running on a standard 230V line. Sizing at 85% efficiency and a power factor of 0.90:
Amps = (5 × 746) ÷ (230 × 0.85 × 0.90) = 3730 ÷ 175.95 = 21.20 Amps
5 HP to Amps 3 Phase
Sizing a three-phase motor rated at 5 HP running on a standard 230V supply. Sizing at a standard 85% efficiency and a power factor of 0.85:
Amps = (5 × 746) ÷ (√3 × 230 × 0.85 × 0.85) = 3730 ÷ 287.82 = 12.96 Amps
Frequently Asked Questions (FAQs)
To convert horsepower (HP) to current in amperes (Amps), convert mechanical power to electrical input power in Watts by multiplying HP by 746 and dividing by efficiency. Then divide this value by voltage and power factor.
For a standard single-phase 230V motor operating at 85% efficiency and a PF of 0.90, 1 HP draws approximately: (1 × 746) ÷ (230 × 0.85 × 0.90) = 4.24 Amps.
Assuming a three-phase 460V system with 88% efficiency and a PF of 0.84, a 30 HP motor draws: (30 × 746) ÷ (√3 × 460 × 0.88 × 0.84) = 22,380 ÷ 588.95 = 38.00 Amps.
For a single-phase 230V circuit running with 85% efficiency and a PF of 0.90, 10 Amps translates to: (10 × 230 × 0.90 × 0.85) ÷ 746 = 2.36 HP.
Assuming a three-phase 460V industrial supply with 88% efficiency and a PF of 0.84, a 25 HP motor draws: (25 × 746) ÷ (√3 × 460 × 0.88 × 0.84) = 18,650 ÷ 588.95 = 31.67 Amps.
