Watt to VA Calculator
This calculator helps you convert real power in Watts (W) to apparent power in Volt-Amps (VA) using the power factor. It is essential for understanding the full load impact in AC electrical systems like UPS, generators, or circuit planning.
Why Convert Watts to VA?
When working with AC electrical systems, it’s crucial to distinguish between real power (Watts) and apparent power (Volt-Amps). While Watts represent the actual usable energy a device consumes or delivers, VA reflects the total load placed on the power supply. This includes both real and reactive components.
Devices like UPS systems, power generators, and transformers are rated in VA, but most appliances report usage in Watts. To correctly size backup power, breakers, or power infrastructure, you must often convert from Watts to VA using the power factor (PF).
Formula: Watts to VA
VA = Watts / Power Factor
- Watts = real, usable power
- Power Factor = efficiency ratio (between 0.1 and 1.0)
Example:
If you have a device rated at 800 Watts with a power factor of 0.8:
VA = 800 / 0.8 = 1000 VA
What Is Power Factor?
Power factor (PF) is the ratio of real power to apparent power. It measures how effectively a device uses the electricity it draws. A PF of 1.0 means all power is being used efficiently, while a lower PF indicates that some power is wasted in reactive components (like inductors or capacitors).
Most resistive loads (e.g., heaters, incandescent lights) have a PF near 1. Devices with motors, transformers, or switching power supplies often have PFs from 0.6 to 0.95 depending on the design.
Why It Matters for UPS and Generators
UPS systems and generators are typically rated in VA. If your load is rated in Watts, you need to convert it to VA to avoid overloading the system. For instance, a 1000W load at 0.8 PF draws 1250VA — so connecting it to a 1000VA UPS would overload it.
Common Conversion Table
| Watts | Power Factor | VA |
|---|---|---|
| 500 | 1.0 | 500 |
| 600 | 0.9 | 667 |
| 800 | 0.8 | 1000 |
| 900 | 0.75 | 1200 |
| 1000 | 0.7 | 1429 |
FAQs
Can I use this for DC systems?
No. In DC systems, Watts = VA because there's no reactive power, and PF = 1. Use this calculator only for AC systems.
What if I don’t know the power factor?
You can estimate based on device type: resistive ≈ 1.0, PCs ≈ 0.9, motors ≈ 0.7–0.85. For accurate results, use a power meter.
Can VA be less than Watts?
No. Since PF ≤ 1, VA is always equal to or greater than Watts.
What happens if I ignore power factor?
You risk overloading your power system. A 1000W device may appear to only need 1000VA, but at 0.7 PF it actually demands ~1430VA.
Conclusion
Accurately converting Watts to VA ensures your UPS, generator, or power supply can truly handle your equipment. It protects your system from overload, improves power planning, and gives you a realistic view of electrical demand. This calculator provides a simple, fast way to perform that conversion using the key input — power factor.