How long will your UPS actually keep things running? Enter your homelab's draw, your UPS rating, and battery age for a realistic estimate.
! Real runtime varies with temperature, inverter efficiency, and load shape. Always configure NUT or apcupsd to trigger shutdown at ~50% remaining.
UPS units are sold by VA (volt-amperes), but your homelab consumes watts. The ratio is the power factor — a number between 0 and 1 that depends on the type of UPS. Most consumer line-interactive units have a power factor around 0.6–0.7. Modern pure-sine units with active PFC compatibility get 0.9. Online double-conversion is closer to 1.0. A 1500 VA APC Back-UPS Pro can really only deliver about 1000W, not 1500W.
If you don't know your battery's amp-hour rating, this calculator estimates it from the VA rating using common 12V battery configurations (most 1000–1500 VA units use one or two 7–9 Ah SLA batteries).