Add the running watts of essential devices, then compare the total with both the UPS watt rating and VA rating. This tool applies a visible 25% planning margin and converts the watt target to VA using the power factor you enter. It does not estimate runtime, startup surge, battery health, waveform compatibility or installation safety.
Add essential load and plan output headroom
The result checks running watts and a transparent VA conversion. It does not predict runtime, surge behavior or installation safety.
Formula and boundaries
Total running load (W) = computer + display + network + other essential watts. Headroom target (W) = total × 1.25. Minimum apparent-power target (VA) = headroom watts ÷ entered power factor.
Schneider Electric's UPS guide recommends checking both watt and VA capacity and describes 20–25% watt headroom. This tool uses the upper end as a visible planning convention, not a universal product guarantee.
How to enter a useful load
- Use running input watts from the device label, power adapter or qualified measurement—not power-supply marketing wattage alone.
- Include the monitor, router, recorder, external storage or other device that must remain on.
- Keep printers, heaters, pumps and motor loads separate unless the UPS manufacturer explicitly supports the load and surge.
- Enter the relevant UPS output power factor from current product documentation; do not guess for a purchase decision.
Sources and further reading
Technical statements were reviewed against these references. External pages may change after our review date.
- Uninterruptible Power Supplies — U.S. Department of Energy
- UPS buying guide: Choose the right battery backup — Schneider Electric