Inputs
Apparent power result
Understanding VA vs Watts
What's the difference?
Watts (W) measure real power — the energy that actually does work in your devices. Volt-Amperes (VA) measure apparent power — the total current and voltage the electrical system must handle, including reactive power that oscillates without doing useful work.
What is power factor?
Power factor (PF) is the ratio of real power to apparent power, ranging from 0 to 1. A PF of 1.0 means all power does useful work. Lower PF means the system draws more current (and requires larger equipment) for the same real power output.
Use Watts
Real power- Calculate energy consumption
- Estimate electricity costs
- Size solar panel arrays
Use VA
Apparent power- Size inverters and UPS units
- Select generators and transfer switches
- Determine wire gauge and breaker size
Common power factor values
- PF 1.0 — Resistive loads: heaters, incandescent bulbs, kettles
- PF 0.9–0.95 — Modern electronics, LED drivers, computers
- PF 0.8 — Mixed household loads (typical default)
- PF 0.6–0.8 — Motors: pumps, compressors, power tools
- PF 0.5–0.7 — Older fluorescent lighting, welding equipment
Real-world solar examples
Sizing an inverter for home loads
Critical loads total 3,200W: fridge (150W), well pump (1,000W), lights (500W), mini-split (1,200W), plus margin. At PF 0.8: 3,200 ÷ 0.8 = 4,000VA minimum inverter. A 5,000VA unit handles surges.
UPS for solar monitoring
Solar monitoring equipment drawing 350W total. At PF 0.6 (typical UPS): 350 ÷ 0.6 = 583VA. You need a 750VA or 1,000VA UPS.
Generator backup sizing
When batteries deplete, a generator must power 5,000W. Generators are rated in VA: 5,000 ÷ 0.8 = 6,250VA. A "5,000W generator" (5kVA) delivers only 4,000W at PF 0.8 — not enough.
When you'll need this conversion
A hybrid solar system needs an automatic transfer switch. The critical load panel draws 7,200W maximum. Converting: 7,200 ÷ 0.8 = 9,000VA. You need a 10kVA transfer switch minimum.
Monitoring and communication equipment draws 2,000W. The UPS must be rated in VA: 2,000 ÷ 0.9 = 2,222VA. A 3,000VA rack-mount UPS provides adequate headroom.
A 5,000W inverter output at 240V: 5,000 ÷ 0.8 = 6,250VA. Current: 6,250 ÷ 240 = 26A, requiring a 30A breaker and 10 AWG wire. VA, not watts, determines wire and breaker sizing.
