Enter both values to calculate volt-amperes
Watts (W)
Power Factor (PF)
Common:
Volt-Amperes (VA)
Result will appear here
Understanding Apparent vs Real Power
VA and watts differ by the power factor:
- Real Power (W) = Apparent Power (VA) × Power Factor
- Apparent Power (VA) = Real Power (W) ÷ Power Factor
- Power Factor ranges from 0 to 1 (1 = perfectly efficient)
For Inverter Sizing
Understanding these relationships 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
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
- Specifying a Transfer Switch — 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.
- Solar Farm Control Room UPS — 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.
- Electrical Panel Calculations — 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.
Solar Tips & Common Mistakes
Always Convert Before Selecting Equipment: Inverters, UPS units, generators, and transfer switches are rated in VA. A 5,000W load does not fit on a 5,000VA inverter unless PF = 1.0 (rare). Always divide watts by expected power factor.
Use Conservative Power Factor Estimates: If exact PF is unknown, use 0.8 for mixed household loads, 0.7 for significant motor loads, and 0.6 for worst-case with older or inductive equipment. Better to slightly oversize than trigger overload protection.
VA Determines Wire and Breaker Sizing: Current in wires is determined by VA, not watts. A 3,000W load at PF 0.7 draws 4,286VA. At 240V = 17.9A, not the 12.5A from watts alone. Undersizing based on watts is a fire hazard.
Solar Calculators
Related Conversion Calculators
Last updated: January 5, 2026
