hp to kVA Converter
A 10 hp motor at 90 percent efficiency and 0.85 power factor needs about 9.7 kVA.
Quick answer: Multiply the horsepower by 0.7457, then divide by the efficiency and the power factor. For example, 10 hp at 90% efficiency and 0.85 PF is 9.748 kVA, 25 hp at 92% efficiency and 0.88 PF is 23.027 kVA and 50 hp at 94% efficiency and 0.9 PF is 44.072 kVA.
The hp to kVA formula
Apparent power in kVA equals the output power in kW divided by efficiency and power factor.
Output power in kW is the horsepower times 0.7457.
Take 10 hp at 90% efficiency and 0.85 PF. 10 × 0.7457 ÷ (0.9 × 0.85) gives 9.748 kVA.
Take 25 hp at 92% efficiency and 0.88 PF. 25 × 0.7457 ÷ (0.92 × 0.88) gives 23.027 kVA.
Shaft power, input power and apparent power
The horsepower on a motor plate is the shaft output. The motor takes more power from the supply because of losses, so you divide by the efficiency.
Power factor is the ratio of real power in kW to apparent power in kVA (Wikipedia: Power factor). So apparent power is real power divided by power factor.
How to convert hp to kVA step by step
- Convert the horsepower to kW by multiplying by 0.7457.
- Divide by the efficiency written as a decimal, such as 0.9.
- Divide by the power factor to get kVA.
- Check the input kW in the last column.
Example 1: 10 hp at 90% efficiency and 0.85 PF
- Start with 10 hp at 90% efficiency and 0.85 PF.
- 10 × 0.7457 ÷ (0.9 × 0.85) = 9.748.
- The apparent power is 9.748 kVA.
10 hp at 90% efficiency and 0.85 PF = 9.748 kVA
Example 2: 25 hp at 92% efficiency and 0.88 PF
- Start with 25 hp at 92% efficiency and 0.88 PF.
- 25 × 0.7457 ÷ (0.92 × 0.88) = 23.027.
- The apparent power is 23.027 kVA.
25 hp at 92% efficiency and 0.88 PF = 23.027 kVA
Example 3: 50 hp at 94% efficiency and 0.9 PF
- Start with 50 hp at 94% efficiency and 0.9 PF.
- 50 × 0.7457 ÷ (0.94 × 0.9) = 44.072.
- The apparent power is 44.072 kVA.
50 hp at 94% efficiency and 0.9 PF = 44.072 kVA
The three examples below use common sizes.
Each one shows the sum in full.
hp to kVA conversion table
| Motor and conditions | Apparent power (kVA) | Input power (kW) |
|---|---|---|
| 1 hp at 85% efficiency and 0.8 PF | 1.097 kVA | 0.8773 kW input |
| 3 hp at 86% efficiency and 0.8 PF | 3.252 kVA | 2.601 kW input |
| 5 hp at 88% efficiency and 0.85 PF | 4.985 kVA | 4.237 kW input |
| 7.5 hp at 89% efficiency and 0.85 PF | 7.393 kVA | 6.284 kW input |
| 10 hp at 90% efficiency and 0.85 PF | 9.748 kVA | 8.286 kW input |
| 15 hp at 91% efficiency and 0.86 PF | 14.293 kVA | 12.292 kW input |
| 20 hp at 92% efficiency and 0.86 PF | 18.85 kVA | 16.211 kW input |
| 30 hp at 93% efficiency and 0.88 PF | 27.335 kVA | 24.055 kW input |
| 40 hp at 94% efficiency and 0.88 PF | 36.059 kVA | 31.732 kW input |
| 50 hp at 94% efficiency and 0.9 PF | 44.072 kVA | 39.665 kW input |
| 75 hp at 95% efficiency and 0.9 PF | 65.412 kVA | 58.871 kW input |
| 100 hp at 95% efficiency and 0.92 PF | 85.32 kVA | 78.495 kW input |
| 150 hp at 96% efficiency and 0.92 PF | 126.65 kVA | 116.52 kW input |
The highlighted row is the default of the calculator. The last column gives kW input.
A quick mental shortcut for hp to kVA
A rough guide for a healthy motor is kVA close to hp. A 20 hp motor needs about 19 kVA.
Always run the full formula before you buy a transformer or generator.
Why kVA is bigger than kW
A supply must carry the apparent power, even though only the real power does work. A low power factor means a larger current for the same job (Wikipedia: Power factor).
That is why generators and transformers are rated in kVA.
Where efficiency fits in
Efficiency is output divided by input. A 90 percent motor turns 90 percent of the input power into shaft power.
The rest becomes heat, so a lower efficiency raises the kVA.
Starting current
This page gives the running load. A motor draws several times more current for a moment when it starts.
Ask an electrician or the motor maker about starting needs before you size a supply.
Quick conversion answers
| Conversion | Result |
|---|---|
| 5 hp at 88% efficiency and 0.85 PF | 4.985 kVA |
| 10 hp at 90% efficiency and 0.85 PF | 9.748 kVA |
| 25 hp at 92% efficiency and 0.88 PF | 23.027 kVA |
| 100 hp at 95% efficiency and 0.92 PF | 85.32 kVA |
Where this conversion is used
Electricians size generators and transformers for motors.
Plant engineers compare supply capacity with motor loads.
Common mistakes to avoid
- Skipping the efficiency. The supply sees more than the shaft power.
- Using the percent as a whole number. Use 0.9, not 90, in the formula.
- Treating kVA as kW. They match only at a power factor of 1.
- Ignoring starting current. The running figure is not the peak.
Related converters
More motor sizes and conditions
2 hp at 85% efficiency and 0.8 PF is 2.193 kVA. 4 hp at 87% efficiency and 0.82 PF is 4.181 kVA. 6 hp at 88% efficiency and 0.84 PF is 6.053 kVA.
12 hp at 90% efficiency and 0.85 PF is 11.7 kVA. 18 hp at 91% efficiency and 0.86 PF is 17.15 kVA. 35 hp at 93% efficiency and 0.89 PF is 31.53 kVA.
60 hp at 94% efficiency and 0.9 PF is 52.89 kVA. 125 hp at 95% efficiency and 0.91 PF is 107.8 kVA. 200 hp at 96% efficiency and 0.92 PF is 168.9 kVA.
Doubling the first number
4 hp at 85% efficiency and 0.8 PF is 4.386 kVA. 8 hp at 87% efficiency and 0.82 PF is 8.362 kVA. 12 hp at 88% efficiency and 0.84 PF is 12.11 kVA.
24 hp at 90% efficiency and 0.85 PF is 23.39 kVA. 36 hp at 91% efficiency and 0.86 PF is 34.3 kVA. 70 hp at 93% efficiency and 0.89 PF is 63.07 kVA.
120 hp at 94% efficiency and 0.9 PF is 105.8 kVA. 250 hp at 95% efficiency and 0.91 PF is 215.6 kVA. 400 hp at 96% efficiency and 0.92 PF is 337.7 kVA.
How power factor changes the answer
10 hp at 90% efficiency and 0.7 PF is 11.84 kVA. 10 hp at 90% efficiency and 0.8 PF is 10.36 kVA. 10 hp at 90% efficiency and 0.9 PF is 9.206 kVA.
10 hp at 90% efficiency and 1 PF is 8.286 kVA.
Frequently asked questions
How do I convert hp to kVA?
Multiply the hp by 0.7457, then divide by the efficiency and the power factor.
How many kVA is a 10 hp motor?
At 90 percent efficiency and 0.85 power factor, about 9.75 kVA.
Why is kVA higher than the horsepower in kW?
Losses and a power factor below 1 both raise the apparent power.
What power factor should I use?
Use the value on the motor plate. If it is missing, 0.85 is a common planning figure.
Is this the starting kVA?
No. It is the running load. Starting needs are higher.
Does this work for single and three phase?
Yes. kVA does not depend on the phase count.
Sources
- Wikipedia: Horsepower (en.wikipedia.org)
- Wikipedia: Power factor (en.wikipedia.org)
