HP to kVA Calculator

How to Convert Horsepower (HP) to Kilovolt-Amperes (kVA)

Horsepower (HP) and kilovolt-amperes (kVA) are measurements of power, but from two different domains. HP measures mechanical output power, while kVA represents electrical apparent power. If you're sizing generators, transformers, or electrical supplies for motors and mechanical equipment, converting HP to kVA is an essential step to ensure you don’t undersize your system or cause performance issues.

What’s the Difference Between HP and kVA?

• Horsepower (HP) is the unit of mechanical power output from motors, pumps, compressors, etc. 1 HP = 746 watts.
• kVA (kilovolt-amperes) is the unit of apparent electrical power. It includes both real power (kW) and reactive power (kVAR).

While HP tells you how much work a machine can do, kVA tells you how much electrical power is required to drive that machine, accounting for inefficiencies and reactive losses in the system.

Formula to Convert HP to kVA

To convert horsepower to kVA, use the following formula:

kVA = (HP × 746) ÷ (Power Factor × Efficiency × 1000)

Where:

• HP = horsepower
• 746 = watts per horsepower
• Power Factor = decimal (typically 0.8–0.95 for motors)
• Efficiency = decimal (typically 0.85–0.95 for motors)

Example:

Convert 50 HP to kVA with PF = 0.9 and efficiency = 0.9:

kVA = (50 × 746) ÷ (0.9 × 0.9 × 1000)
     = 37300 ÷ 0.81 × 1000
     ≈ 46.05 kVA

You would need a 46 kVA electrical supply to power a 50 HP motor at 90% efficiency and 0.9 PF.

Efficiency and Power Factor Explained

Efficiency

Efficiency refers to how much of the electrical energy input is converted into mechanical power output. A typical electric motor has an efficiency between 85% and 95%. A more efficient motor draws less electrical power for the same mechanical output.

Power Factor (PF)

Power factor is a measure of how effectively the electrical power is being used. Motors often have a lagging power factor (0.8–0.95), especially under partial load. Lower PF means more apparent power (kVA) is needed to produce the same real power (kW), and thus to drive a given HP.

Efficiency and PF Chart (Typical Ranges)

Common Applications for HP to kVA Conversion

• Generator sizing for industrial motors
• Transformer capacity planning for HVAC, pump, or conveyor systems
• Electrical design for motor control centers (MCCs)
• Determining starter or VFD size for high-inrush motors

Common Mistakes

• Assuming 100% efficiency: Always include realistic efficiency (typically 0.85–0.95)
• Ignoring power factor: This results in significant underestimation of kVA requirement
• Using nameplate HP without load consideration: Always account for peak or startup loads

Best Practices

• Use a conservative power factor (e.g., 0.85) if unknown
• Size for peak HP or include a startup surge buffer
• Consult manufacturer motor datasheets whenever available
• Round up your final kVA result to avoid undersizing

FAQ – HP to kVA Conversion

Is HP the same as kW?

No. 1 HP = 746 watts = 0.746 kW. HP is mechanical, kW is electrical real power. To convert HP to kW: HP × 0.746

Can I convert HP to kVA directly?

Yes, with known power factor and efficiency. Use: kVA = (HP × 746) ÷ (PF × Efficiency × 1000)

Why does power factor matter?

Because it tells how much of the total current is doing useful work. A lower PF means you need more apparent power (kVA) to produce the same mechanical output.

What size generator do I need for a 100 HP motor?

Assuming PF = 0.9 and efficiency = 0.9:
kVA = (100 × 746) ÷ (0.9 × 0.9 × 1000) ≈ 92 kVA
So a generator rated ≥ 92 kVA would be required.

Can I use this for diesel generators?

Yes — diesel, gas, or hybrid — as long as you know the HP requirement and load characteristics.

What if I only know the kW?

You can first convert kW = HP × 0.746, then convert to kVA using kVA = kW ÷ PF.

How much buffer should I allow?

It’s best to add 10–25% extra kVA when sizing equipment, to account for startup current and future load growth.

Conclusion

Whether you're specifying electrical infrastructure for industrial equipment, irrigation systems, or HVAC motors, the HP to kVA conversion gives you a safe starting point for generator or transformer sizing. Underestimating the kVA requirement can lead to overheating, voltage drops, or tripping circuits. Overestimating leads to overspending.

Use our HP to kVA Calculator above to get accurate, real-world estimates based on power factor and efficiency. Then round up slightly and consult with a licensed electrician or engineer for final specification.