Load (Power Draw)
Battery Capacity
Efficiency
About this tool
UPS runtime estimates are based on usable watt-hours (total capacity × depth of discharge × inverter efficiency) divided by the load in watts. Real-world runtime is typically shorter due to the Peukert effect - lead-acid batteries lose capacity at higher discharge rates - and battery age or temperature. Use this estimate for capacity planning and right-sizing, then validate against your UPS manufacturer's runtime curves. A common best practice is to target at least 10–15 minutes of runtime for an orderly shutdown, or 30–60 minutes if you rely on generator start-up time.