What is the difference between kW and kVA?

kW (kilowatts) is real power — the actual work done. kVA (kilovolt-amperes) is apparent power, which includes the reactive component due to inductive loads. kVA = kW / power factor.

What power factor should I use?

Most AC induction motors operate between 0.80 and 0.95 power factor at full load. If unknown, use 0.85 as a conservative estimate. Check the motor nameplate for the rated PF.

Why does efficiency matter?

Motor efficiency accounts for internal losses (heat, friction). A 90% efficient motor drawing 10 HP of shaft output actually consumes more electrical input. The formula divides by efficiency to get true electrical input.

What is 1 mechanical horsepower in watts?

1 mechanical horsepower equals exactly 745.7 watts. For calculations this is rounded to 746 W. Electrical horsepower (used in the US for motors) is also defined as 746 W.

How do I size a generator for a motor?

Calculate running kVA using this tool and add 20–25% margin for continuous operation. Direct-on-line motors draw 5–7× rated current at startup, typically requiring a generator with 2–3× running kVA to handle starting surge unless a soft starter or VFD is used.

Horsepower to kVA Calculator

Convert horsepower (HP) to kilovolt-amperes (kVA) instantly by entering horsepower, efficiency, and power factor.

Input Values

Horsepower (HP)

Motor Efficiency (%) — check nameplate, or use 90% if unknown

Power Factor (PF) — 0.01 to 1.00

Apparent Power

—

kilovolt-amperes (kVA)

Calculation Breakdown

Horsepower	—
Watts per HP	746 W
Total input power (kW)	—
Motor efficiency	—
Power factor	—
Result (kVA)	—

Formula: kVA = (HP × 746) ÷ (Efficiency × PF × 1000)

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Summary

This calculator converts motor horsepower (HP) to kilovolt-amperes (kVA). It factors in motor efficiency and power factor (PF) to calculate the electrical apparent power drawn by equipment. The result is useful for sizing transformers, generators, and electrical supply panels.

How it works

Enter the horsepower (HP) rating of the motor or equipment (1 HP = 746 W).
Enter the motor efficiency percentage (check nameplate, or use 90% if unknown).
Enter the operating power factor (PF), typically 0.80 to 0.95 for AC induction motors.
The calculator applies the formula: kVA = (HP × 0.746) / (Efficiency × PF) and displays apparent power.

Use cases

Size a generator or transformer for an electric motor.
Determine apparent power for electrical panel design.
Convert motor nameplate HP to kVA for utility billing estimates.
Calculate generator capacity needed to start a motor.
Verify electrical supply ratings match motor requirements.
Convert pump or compressor HP ratings to electrical load.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu