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UPS sizing calculator

List what will plug into the UPS. You'll get the minimum watt and VA rating to look for.

Equipment on the UPS
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Preset watts are rough starting points. Use the number on each device's power supply label or datasheet, or a measured reading from a metered PDU, for a real plan. For a PoE switch, include the power it sends to devices.

UPS power factor

A UPS has two ratings, VA and watts, and you must stay under both. The power factor is the ratio between them; check the UPS datasheet.

Watts, VA and headroom

Every UPS lists two ratings. Watts is the real power it can supply; VA is apparent power. Your load has to fit under both. A UPS running near 100% has almost no runtime and no room for growth, so size for about 75–80% of its watt rating.

Runtime is a separate question. Two UPS units with the same rating can run very different times on the same load, depending on their battery packs. Check the runtime chart for the specific model.