HP to kVA Calculator
Convert motor horsepower to kVA using the motor efficiency and power factor. Enter the hp, efficiency, and power factor to get the apparent power in kVA for sizing a generator, transformer, or cable.
How to Convert HP to kVA
To convert a motor's horsepower to kVA, divide the power by both the motor efficiency and the power factor after converting to kilowatts. Horsepower is the mechanical output at the shaft, while kVA is the apparent electrical power the motor draws.
- kVA = apparent power in kilovolt-amperes
- hp = motor horsepower (shaft output)
- 0.746 = kilowatts in one horsepower
- η = motor efficiency (as a decimal)
- PF = power factor
Example: a 20 hp motor at 90% efficiency and 0.85 PF is (20 × 0.746) / (0.90 × 0.85) = 19.5 kVA.
The 0.746 converts horsepower to kilowatts, and dividing by efficiency and power factor steps up from mechanical output to the apparent power the supply must provide. For the reverse direction, our kVA to HP calculator runs the same chain backward.
Why you need efficiency and power factor
A motor's horsepower is the mechanical work at the shaft, not the electricity it draws, and two things sit between them. Efficiency accounts for the electrical input being larger than the mechanical output; a 90 percent efficient motor pulls about 11 percent more real power than it delivers. Power factor then accounts for apparent power (kVA) being larger than real power (kW), because a motor also draws reactive current to build its magnetic field. Divide by both and you get the kVA a generator, transformer, or cable has to supply. Leave them out and you undersize the equipment.
Is 1 hp equal to 1 kVA?
Roughly, for a typical motor. At 90 percent efficiency and a 0.85 power factor, 1 hp works out to about 0.98 kVA, so a motor's horsepower and its kVA are close. It is only a rule of thumb: with a poor power factor of 0.7 the same 1 hp needs about 1.2 kVA, and in the ideal case of 100 percent efficiency and unity power factor it is just 0.746 kVA. Always use the actual nameplate efficiency and power factor for sizing.
How many kVA is 20 HP?
About 19.5 kVA for a typical motor at 90 percent efficiency and a 0.85 power factor. The exact figure depends on those two values; a lower efficiency or power factor raises the kVA. Apparent power in kVA combines real power (kW) with reactive power, and our Amps to kVA calculator explains the power triangle behind it.
Typical efficiency and power factor by motor size
If you do not have the nameplate, these ranges are a reasonable starting point. Motor efficiency classes are set by IEC 60034-30-1 (the IE1 to IE4 codes) and by NEMA Premium in the US.
| Motor size | Efficiency | Full-load power factor |
|---|---|---|
| Under 5 hp | 80 to 87% | 0.75 to 0.80 |
| 10 to 50 hp | 88 to 93% | 0.82 to 0.87 |
| Over 100 hp | 94 to 96% | 0.85 to 0.90 |
Both figures fall at part load, especially the power factor, which is why a lightly loaded motor draws a surprising amount of kVA.
HP to kVA conversion chart
These use a typical motor efficiency of 90 percent and a 0.85 power factor. Your motor nameplate values may differ, so enter them above for an exact figure.
| Horsepower | Apparent power (kVA) |
|---|---|
| 1 hp | 0.98 kVA |
| 1.5 hp | 1.46 kVA |
| 5 hp | 4.88 kVA |
| 10 hp | 9.75 kVA |
| 12 hp | 11.70 kVA |
| 15 hp | 14.63 kVA |
| 20 hp | 19.50 kVA |
| 25 hp | 24.38 kVA |
| 50 hp | 48.76 kVA |
| 100 hp | 97.52 kVA |
The kVA scales directly with horsepower at a fixed efficiency and power factor, so doubling the hp doubles the kVA. Change either value and every row shifts; a poorer power factor means more kVA for the same hp.
Sizing a generator or transformer for a motor
Generators, transformers, and UPS units are rated in kVA because they must supply the apparent power, not just the real power. Converting a motor's horsepower to kVA gives the minimum rating. US motors are rated in horsepower under NEMA MG 1, and IEC motors in kilowatts under IEC 60034-1. For a direct-on-line start you add margin, since a motor can pull several times its running kVA for a few seconds at startup, so a 25 hp pump at 24.4 kVA running is often fed from a 30 kVA source. For the real power in kilowatts instead, see HP to kW, and to go from kW to kVA, kW to kVA.
Does three-phase change the HP to kVA formula?
No. The formula kVA = (hp × 0.746) / (efficiency × power factor) is the same for single-phase and three-phase motors, because kVA is apparent power and does not depend on the number of phases. The phase count and voltage only matter when you find the line current in amps from the kVA. So a 20 hp three-phase motor and a 20 hp single-phase motor need the same kVA at the same efficiency and power factor.
Limitations and safe use
The result is the running kVA at the efficiency and power factor you enter. It does not include motor starting inrush, which can be five to eight times the running current on a direct-on-line start, so size the supply and protection with that margin and per NEC Article 430 for the motor circuit. Use nameplate efficiency and power factor where you have them; the defaults are estimates, not a design value. This tool sizes the power rating only, not a substitute for a circuit design by a qualified electrician.
Frequently Asked Questions
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How many kVA is 20 HP?
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Why does HP to kVA need efficiency and power factor?
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