Find the minimum VA rating for a UPS to handle your load, based on watts and power factor.
A UPS (uninterruptible power supply) — called "nobreak" in Brazil — is rated in VA (volt-amperes), not watts. The relationship is watts = VA × power factor. Consumer UPS units typically have a power factor of 0.5-0.7, meaning a 1000 VA unit delivers only 500-700 watts of real power.
This calculator divides your total load in watts by the power factor to give the minimum VA rating. But VA alone does not tell you how long the battery lasts — that depends on the battery size and the actual load. Always check the manufacturer runtime chart at your specific wattage.
A practical rule: oversize by at least 30% to leave room for power spikes (a laser printer or a compressor starting up draws several times its steady wattage for a fraction of a second) and to extend battery life, since running a UPS at full load ages the battery faster.
VA = watts / power factor. Runtime depends on battery capacity and load — consult the manufacturer chart.
Check the UPS spec sheet. Consumer units are typically 0.5-0.7. Enterprise/server UPS units often have a power factor of 0.8-0.9.
Not necessarily — VA is the maximum load capacity, and runtime depends on the battery size. A 1500 VA unit with a small battery may give less runtime than an 800 VA unit with a large battery.
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