Enter values
Watts result
Understanding apparent vs real power
Volt-amperes (VA) measures apparent power — the total current × voltage flowing through a circuit. Watts (W) measures real power — the portion that actually does useful work. The difference is the power factor, which accounts for reactive power drawn by motors and electronics.
Key formulas
When to use each unit
Use VA
Apparent- Size inverters and UPS units
- Select transfer switches
- Determine wire and breaker sizing
Use Watts
Real- Match appliance power consumption
- Calculate electricity costs
- Size solar panel arrays
Power factor by load type
- Resistive loads (PF ~1.0) — heaters, kettles, incandescent bulbs. VA ≈ Watts.
- Electronics (PF 0.55–0.95) — computers, LED drivers, phone chargers. Modern PSUs often include PFC.
- Motors (PF 0.5–0.85) — pumps, compressors, power tools. Inductive loads draw significant reactive power.
- Mixed household (PF ~0.8) — typical residential load combining all types. Use 0.8 if unknown.
For inverter sizing
Understanding VA vs watts helps you:
- Size inverters correctly — always size for VA, not watts
- Understand UPS ratings — VA tells the full story
- Account for motors — they have low power factor (0.6–0.8)
- Plan for inductive loads — electronics often have PF around 0.9
Real-world solar examples
A 3,000VA inverter with power factor 0.8 delivers a maximum of 2,400W usable power. To keep solar matched, you need at least 2,400W of panels at peak.
Resistive loads (lights, heaters) at PF ~1.0: 1,000VA = 1,000W. A 1,500W table saw at PF ~0.7 draws ~2,143VA. A 5,000VA inverter at PF 0.8 delivers 4,000W, but motor loads can push VA above 5,000 even when watts are under 4,000.
A 1,000VA UPS at PF 0.6 delivers only 600W real power. At PF 0.9: 900W. A 500W monitoring setup at PF 0.7 needs 714VA — a 1,000VA/0.6PF UPS barely covers it.
When you'll need this conversion
- Buying an off-grid inverter — Inverters are marketed in VA, but appliances are rated in watts. A 2,000VA inverter does not deliver 2,000W — multiply by power factor (0.8 typical, 0.6 for budget units) to find actual usable watts.
- Calculating true hybrid inverter load — A 5,000VA hybrid inverter with PF 0.8 delivers 4,000W. Adding 4,500W of appliances triggers overload protection. The VA-to-watts conversion reveals the mismatch before it causes problems.
- Comparing inverter brands — Brand A sells a “5000W” inverter (5,000VA at PF 0.8 = 4,000W real). Brand B sells a “5000W” at PF 1.0 = 5,000W real. Always check the spec sheet for both VA and watt ratings.
