VA and watts both measure electrical power, but they describe different things. VA (volt-amperes) is apparent power: the product of voltage multiplied by current in the circuit. Watts is real power: the actual energy consumed and converted to heat, light, or work. The difference matters because some equipment stores energy temporarily rather than consuming it immediately.
In a purely resistive load like a heater or incandescent bulb, VA and watts are equal. But devices with reactive components like inductors or capacitors (found in motors, transformers, and power supplies) draw more current than they actually use. This gap between apparent and real power is expressed as power factor, typically 0.7 to 0.9 for computer equipment.
When shopping for uninterruptible power supplies (UPS) or surge protectors, manufacturers often advertise VA ratings because the numbers look larger and more impressive. A 1500 VA UPS might only deliver 900-1000 watts of real power, depending on the power factor. This misleads buyers into thinking they have more capacity than they actually do.
To find real power output, multiply the VA rating by the power factor, usually printed in the specifications. If power factor is not listed, assume 0.7 to 0.8 for conservative planning. Always add up the actual watt consumption of your devices (check their labels or use a plug-in meter) rather than relying on VA ratings. This prevents overloading your UPS during a mains failure and ensures connected equipment actually receives sufficient power when you need it most.