Watts to kVA Calculator
Enter real power in watts and power factor to calculate apparent power in kVA instantly. Essential for sizing generators, UPS systems and transformers.
How do you convert watts to kVA?
Divide watts by the power factor and then by 1000: kVA = W ÷ (PF × 1000). A 1500 W load at PF 0.8 equals 1500 ÷ (0.8 × 1000) = 1.875 kVA. Because apparent power is always ≥ real power, a generator or UPS rated in kVA must be chosen based on this larger figure — not the watts alone.
Power factor represents the efficiency of power use in an AC circuit. Resistive loads (heaters, incandescent lamps) have PF = 1.0 so kVA = kW. Inductive loads (motors, transformers) typically have PF 0.7–0.95, meaning the apparent power is significantly higher than the real power.
Watts to kVA Conversion Table
| Watts (W) | PF 0.7 | PF 0.8 | PF 0.9 | PF 1.0 |
|---|---|---|---|---|
| 500 W | 0.714 kVA | 0.625 kVA | 0.556 kVA | 0.500 kVA |
| 1000 W | 1.429 kVA | 1.250 kVA | 1.111 kVA | 1.000 kVA |
| 1500 W | 2.143 kVA | 1.875 kVA | 1.667 kVA | 1.500 kVA |
| 2000 W | 2.857 kVA | 2.500 kVA | 2.222 kVA | 2.000 kVA |
| 5000 W | 7.143 kVA | 6.250 kVA | 5.556 kVA | 5.000 kVA |
| 10000 W | 14.29 kVA | 12.50 kVA | 11.11 kVA | 10.00 kVA |
Formula
Where: kVA = apparent power in kilovolt-amps, W = real power in watts, PF = power factor (0–1).
Alternatively expressed as: kVA = kW ÷ PF. If you already have kW, use the kW to kVA calculator directly.
Sizing Transformers for Real-World Loads
When you know the real power (Watts) your equipment requires, you must convert to Apparent Power (kVA) to order the correct size transformer or generator. Dividing Watts by the Power Factor (PF) ensures the equipment isn't undersized:
- Sizing for an 8,000 W Industrial Motor (PF = 0.8):
kVA = 8,000 ÷ (0.8 × 1,000) = 10 kVA. The motor only does 8 kW of mechanical work, but draws 10 kVA of current from the transformer. You must buy at least a 10 kVA transformer. - Sizing for a 4,500 W Electric Heater (PF = 1.0):
kVA = 4,500 ÷ (1.0 × 1,000) = 4.5 kVA. Purely resistive loads have no reactive power, so real power (kW) equals apparent power (kVA). - Sizing for an LED Lighting Array (2,000 W, Cheap drivers PF = 0.6):
kVA = 2,000 ÷ (0.6 × 1,000) = 3.3 kVA. The poor power factor means the wiring and transformer must handle 65% more current than the actual wattage suggests.
Frequently Asked Questions
Use the formula kVA = W ÷ (PF × 1000). You need the power factor of your load. If unknown, 0.8 is a common conservative assumption for mixed AC loads.
Real power (watts) is the energy actually consumed as heat, light or work. Apparent power (kVA) is the total power the supply delivers, including the reactive portion that flows back and forth in inductive circuits. A generator must be sized to the apparent power, not just the real power.
Power factor is the ratio of real power to apparent power (PF = kW ÷ kVA). Without it, you cannot determine how much of the apparent power is doing useful work. A purely resistive load (PF = 1) has kVA = kW, but a motor at PF = 0.8 needs 25 % more apparent power than its real-power rating.
It depends on the power factor. At PF 0.8: 2000 ÷ (0.8 × 1000) = 2.5 kVA. At PF 0.9: 2000 ÷ (0.9 × 1000) ≈ 2.22 kVA. At PF 1.0: 2000 ÷ 1000 = 2.0 kVA.
No. Apparent power (kVA) is always greater than or equal to real power (kW) because PF is always ≤ 1. If kVA equalled kW, the power factor would be 1.0, meaning a purely resistive load with no reactive component.
If my equipment uses 5,000 Watts, can I use a 5 kVA transformer?
Only if the power factor of your equipment is exactly 1.0 (like a resistive heater). If you are running motors, computers, or LED drivers with a power factor of 0.8, your 5,000 W load actually demands 6.25 kVA of apparent power, which will overload a 5 kVA transformer.