Convert motor horsepower to kVA (kilovolt-amperes). Enter HP, efficiency, and power factor to get accurate apparent power for generator and transformer sizing.
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Verified: NEC 2023 — Motor Power and Apparent Power Standards — April 2026
HP
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Motor rated horsepower
%
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Typical NEMA motors: 85-95%. Use 90% if unknown.
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AC motors: 0.80-0.95 at full load. Use 0.85 if unknown.
Convert motor horsepower to kVA (kilovolt-amperes). Enter HP, efficiency, and power factor to get accurate apparent power for generator and transformer sizing.
Apparent Power (kVA)
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⚠️ Disclaimer: These calculations are for planning purposes. Always verify against nameplate data and consult a licensed electrical engineer for generator, transformer, and motor system design. Actual starting kVA can be 3-7x running kVA for direct-on-line motor starts.
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Sources & Methodology
✓ Formulas and reference data verified against authoritative sources listed below.
IEEE power systems reference for kVA, kW, kVAR power triangle calculations
Methodology: Output kW = HP x 0.7457. Input kW = Output kW / Efficiency. kVA = Input kW / Power Factor. kVAR = sqrt(kVA^2 - kW^2). 1 HP = 745.7 watts (IEC). kVA is apparent power used for generator and transformer sizing. kW is real power billed by the utility.
⏱ Last reviewed: April 2026
How to Convert Horsepower to kVA
kVA (kilovolt-amperes) is the apparent power that electrical equipment must supply to a motor. It is always larger than the motor's actual power output (HP) because it accounts for both efficiency losses and power factor. Generators, transformers, and UPS systems are rated in kVA, making this conversion essential for sizing those devices correctly.
The HP to kVA Formula
kVA = (HP x 0.7457) / (Efficiency x Power Factor). Example: 10 HP motor, 90% efficiency, 0.85 PF: Output kW = 10 x 0.7457 = 7.457 kW. Input kW = 7.457 / 0.90 = 8.286 kW. kVA = 8.286 / 0.85 = 9.748 kVA. A 10 kVA generator is sufficient with some headroom.
kVA vs kW vs kVAR — The Power Triangle
These three quantities form a right triangle: kVA (hypotenuse) = apparent power. kW (adjacent) = real power (does actual work). kVAR (opposite) = reactive power (stored in inductors/capacitors, does no useful work). Power factor = kW / kVA = cos(phase angle). A PF of 1.0 means kVA = kW (perfectly efficient, resistive load).
Why kVA Matters for Generator Sizing
When you size a generator for a motor, you must use kVA not kW. A 10 kW generator at 0.8 PF can only supply 8 kW of real power to an inductive motor load. The generator must handle the full apparent power draw. Always size generators at 125% of the calculated motor kVA per NEC guidelines.
Power Factor Correction
Low power factor (below 0.85) means motors draw more apparent power (kVA) than necessary, requiring larger generators and conductors. Power factor correction capacitors can raise PF toward 1.0, reducing kVA demand. Utilities often charge a PF penalty for industrial loads below 0.85 or 0.90.
kVA = (HP x 0.7457) / (Efficiency x Power Factor)
1 HP = 0.7457 kW (mechanical). Input kW = Output kW / Efficiency. kVA = Input kW / PF. kVAR = sqrt(kVA^2 - kW^2). Power Factor = kW / kVA. Example: 5 HP, 90% eff, PF 0.85: kVA = (5 x 0.7457) / (0.90 x 0.85) = 3.729 / 0.765 = 4.87 kVA.
Typical HP to kVA Values (90% Eff, 0.85 PF)
HP
kW Output
kW Input (90% eff)
kVA (PF 0.85)
Min Generator
1
0.746
0.829
0.975
1.5 kVA
2
1.491
1.657
1.950
2.5 kVA
5
3.729
4.143
4.874
6.0 kVA
10
7.457
8.286
9.748
12.5 kVA
20
14.914
16.571
19.495
25 kVA
50
37.285
41.428
48.739
62.5 kVA
100
74.570
82.856
97.478
125 kVA
⚡ Generator Sizing Rule: Always size a generator at 125% of the total calculated kVA to handle motor starting currents (which can be 6-8x running current) and future load additions. For multiple motors on one generator, add all motor kVA values and apply the 125% factor to the total.
Frequently Asked Questions
kVA = (HP x 0.7457) / (Efficiency x Power Factor). For 5 HP at 90% efficiency and 0.85 PF: kVA = (5 x 0.7457) / (0.90 x 0.85) = 3.729 / 0.765 = 4.87 kVA.
kW (kilowatts) is real power that does actual work. kVA (kilovolt-amperes) is apparent power — the total power drawn from the supply including reactive power. kVA = kW / Power Factor. For PF = 1.0, kVA = kW. For inductive motors with PF = 0.85, kVA is about 18% higher than kW.
10 HP at 90% efficiency and 0.85 PF: kVA = (10 x 0.7457) / (0.90 x 0.85) = 7.457 / 0.765 = 9.748 kVA. A 10 kVA generator handles this with minimal headroom; a 12.5 kVA unit is recommended.
Generators produce both real power (kW) and reactive power (kVAR). The generator must supply the total apparent power (kVA) to the load. Rating a generator in kW alone ignores the reactive component that the generator must still produce, which can overload the alternator even if the real power is within limits.
Use the motor nameplate power factor if available. If unknown: fully loaded NEMA motors typically have PF of 0.85 to 0.90. At 75% load: 0.80 to 0.87. At 50% load: 0.72 to 0.80. Power factor decreases significantly at light load, which is why oversized motors are inefficient.
HP = kVA x Efficiency x PF / 0.7457. For 10 kVA at 90% efficiency and 0.85 PF: HP = 10 x 0.90 x 0.85 / 0.7457 = 7.65 / 0.7457 = 10.26 HP.
kVAR (kilovolt-amperes reactive) is the reactive power component consumed by the motor's inductive windings. It does no useful work but must be supplied by the generator. kVAR = sqrt(kVA^2 - kW^2). Power factor correction capacitors cancel kVAR, reducing kVA demand.
Add up the kVA of all motors running simultaneously. Then multiply by 1.25 for the largest motor's starting current allowance. Example: three 5 HP motors (4.87 kVA each) = 14.6 kVA running, plus starting allowance for largest: 14.6 + (4.87 x 3) = 29.2 kVA minimum generator.
1 HP at 90% efficiency and 0.85 PF: kVA = 0.7457 / (0.90 x 0.85) = 0.7457 / 0.765 = 0.975 kVA. Approximately 1 kVA of generator capacity per 1 HP of motor at standard efficiency and power factor.
No. HP is the mechanical output at the motor shaft. The electrical input (kW) is always higher due to efficiency losses (heat, friction). A 10 HP (7.457 kW output) motor at 90% efficiency draws 8.286 kW from the grid. The generator must supply the input kW, not the output HP converted directly.