Motor HP / kW Converter
Enter horsepower or kilowatts, along with motor voltage and efficiency, to get the equivalent value and estimated full-load amperage.
Reviewed by the ToolNestr Editorial Team — July 2026
How motor power conversion works
Motor power is measured in both horsepower (HP) and kilowatts (kW). One mechanical horsepower equals 745.7 watts (0.7457 kW). The conversion is straightforward: kW = HP × 0.7457 (mechanical) or multiply by 0.746 (electrical). To convert kW to HP, divide by the same constant.
Full-load amperage (FLA) for three-phase motors is calculated as: FLA = (kW × 1000) / (V × PF × η × √3), where PF is power factor and η is efficiency. For single-phase motors, the √3 factor is omitted.
Worked examples
What different motor sizes mean
Common NEMA standard motor sizes span from fractional HP to large industrial motors.
Maintenance Engineer
Verify motor nameplate ratings, calculate expected currents, and plan electrical infrastructure for replacement motors.
Plant Manager
Estimate power consumption and operating costs of motors for budgeting and energy efficiency optimization projects.
Electrician
Size feeders, breakers, and contactors correctly by calculating full-load amperage from motor nameplate data.
Equipment Specifier
Convert between HP and kW to specify motors correctly for international projects and equipment procurement.
| HP | kW (mech) | kW (elec) | FLA 230V 3ph | FLA 460V 3ph | Efficiency |
|---|---|---|---|---|---|
| 0.5 | 0.37 | 0.37 | 1.6 A | 0.8 A | 77% |
| 1 | 0.75 | 0.75 | 2.8 A | 1.4 A | 80% |
| 5 | 3.73 | 3.73 | 12.0 A | 6.0 A | 85% |
| 10 | 7.46 | 7.46 | 22.5 A | 11.2 A | 88% |
| 25 | 18.65 | 18.65 | 53.0 A | 26.5 A | 91% |
| 50 | 37.30 | 37.30 | 103.0 A | 51.5 A | 92% |
| 100 | 74.60 | 74.60 | 199.0 A | 99.5 A | 94% |
| 500 | 373.00 | 373.00 | 980.0 A | 490.0 A | 95% |
How to use the Motor HP / kW Converter
Enter power rating
Choose whether to enter HP or kW. If entering HP, select mechanical or electrical HP type for precise conversion.
Enter motor parameters
Fill in voltage, phase (single or three), efficiency, and power factor. These are used for full-load amp calculation.
Read all results
The calculator shows the converted value (HP or kW), full-load amperage, and apparent power in kVA — all updated in real time.
Tips for motor power conversion
Always use mechanical HP for engines
Mechanical HP (745.7 W) is the standard for engines, turbines, and other non-electric power sources. Electrical HP (746 W) is only used for electric motor ratings. The calculator supports both.
Check motor nameplate for exact values
The full-load amp calculation is an estimate. For precise values, always refer to the motor nameplate or manufacturer datasheet. Actual FLA can vary by up to 10% depending on the motor design.
Account for service factor
NEMA motors have a service factor (typically 1.0 to 1.25) that indicates how much continuous overload the motor can handle. A 1.15 service factor means the motor can run at 115% of rated load. Size protective devices accordingly.
Verify voltage compatibility
Motors designed for 460V can typically operate at 460\u00b110% (414\u2013506V). Using the wrong voltage reduces efficiency, increases current, and may damage the motor. Dual-voltage motors can be wired for 230V or 460V.
HP vs kW
Horsepower and kilowatts are both units of power. One mechanical horsepower equals 745.7 watts (0.7457 kW), while one electrical horsepower equals exactly 746 watts (0.746 kW). The conversion is straightforward: multiply HP by 0.7457 (mechanical) or 0.746 (electrical) to get kW, or divide kW by the same constants to get HP. Horsepower is still widely used in North America, while kW is the international (SI) standard.
FLA calculation formula
Full-load amperage (FLA) is calculated from real power, voltage, efficiency, and power factor. For single-phase motors: FLA = (kW \u00d7 1000) / (V \u00d7 PF \u00d7 \u03b7). For three-phase motors: FLA = (kW \u00d7 1000) / (V \u00d7 PF \u00d7 \u03b7 \u00d7 \u221a3). The \u221a3 factor (approximately 1.732) accounts for the phase relationship in three-phase power.
Motor efficiency
No motor converts 100% of electrical input to mechanical output. Losses come from resistive heating in windings (I\u00b2R), magnetic hysteresis, eddy currents, bearing friction, and windage. NEMA Premium Efficiency motors typically achieve 90\u201396% efficiency. The Department of Energy mandates minimum efficiency standards that vary by motor size and type.
NEMA standards
NEMA MG-1 defines standard motor ratings, performance characteristics, frame sizes, and testing methods. Standard NEMA frame sizes (e.g., 143T, 184T, 256T, 364T, 445T) correspond to specific shaft heights, centerline dimensions, and mounting configurations. IEC motors use metric frame designations. Always verify NEMA or IEC frame compatibility when replacing a motor.
Frequently asked questions
What is the difference between mechanical HP and electrical HP?
Mechanical horsepower (HP) is defined as 745.7 watts (550 ft·lb/s). Electrical horsepower is defined as exactly 746 watts. The difference is negligible for most practical purposes, but electrical HP is used specifically for electric motor ratings while mechanical HP is used for engines and turbines.
How do I convert HP to kW?
For mechanical HP: kW = HP × 0.7457. For electrical HP: kW = HP × 0.746. For example, a 10 HP mechanical motor equals 7.457 kW, and a 10 HP electrical motor equals 7.46 kW.
How do I convert kW to HP?
For mechanical HP: HP = kW / 0.7457. For electrical HP: HP = kW / 0.746. For example, 7.5 kW equals approximately 10.06 mechanical HP or 10.05 electrical HP.
How do I calculate full-load amps for a motor?
For single-phase: FLA = (kW × 1000) / (V × PF × η). For three-phase: FLA = (kW × 1000) / (V × PF × η × √3). Where V is voltage, PF is power factor, and η is efficiency (as a decimal).
What is motor efficiency?
Motor efficiency (η) is the ratio of mechanical output power to electrical input power. Typical efficiencies range from 75% for small fractional-HP motors to 95%+ for large premium-efficiency motors. Higher efficiency means lower operating costs.
What is power factor and why does it matter?
Power factor (PF) is the ratio of real power (kW) to apparent power (kVA). Induction motors typically have a PF of 0.7–0.9 at full load. Low power factor means higher current for the same real power, increasing distribution losses and potentially incurring utility penalties.
What are NEMA standard motor sizes?
NEMA standardizes motor horsepower ratings: fractional (1/4, 1/3, 1/2, 3/4 HP) and integral (1, 1.5, 2, 3, 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150, 200, 250, 300, 350, 400, 450, 500 HP).
What voltage ratings do motors use?
Common motor voltages include 115V, 208V, 230V, 460V, 575V for single and three-phase. High-voltage motors may use 2300V, 4160V, or 6600V. The calculator supports any voltage input for maximum flexibility.
How can I reduce motor starting current?
Motors draw 5–8× their full-load current during starting. Methods to reduce inrush include: soft starters, variable frequency drives (VFDs), star-delta starting, autotransformer starting, and reactor starting. VFDs provide the most control and energy savings.
What is the difference between single-phase and three-phase motors?
Single-phase motors are used in residential and light commercial applications up to about 5 HP. Three-phase motors are more efficient, have better starting torque, and are used for industrial applications above 1 HP. Three-phase motors also have a higher power-to-weight ratio.
Sources & references
This tool uses standard formulas and reference values from:
- • NFPA 70 — National Electrical Code (NEC), conduit fill, box fill and conductor ampacity. nfpa.org
- • IPC-2221, Generic Standard on Printed Board Design (trace width / current). ipc.org
- • NIST reference constants and unit definitions; IEEE standards where applicable. nist.gov
For educational and preliminary use. Verify against full engineering calculations and the governing standard before any real design.