UPS Runtime Calculator – Battery Backup Duration
Calculate how long a UPS battery will last at any load.
About This Calculator
Calculate how long a UPS battery will last at any load. Use the calculator above for instant results.
Worked Examples
- UPS: ~1,350W capacity | 500W = 37% load
- Runtime: ~18.2 minutes
Answer: ~18 minutes
- 600W = 20% load | Runtime: ~27 minutes
Answer: ~27 minutes
- 40% load | Runtime: ~17 minutes
Answer: ~17 minutes
Who Uses This Calculator?
Right-size UPS for server rooms.
Plan UPS capacity and runtime.
Power backup planning.
Business continuity power planning.
Common Mistakes to Avoid
❌ Battery runtime is approximate
UPS runtime calculators give estimates. Actual runtime depends on battery age, temperature, load type, and power factor.
❌ Batteries degrade
A 5-year-old battery may have 50-70% of original capacity. Replace UPS batteries every 3-5 years.
Frequently Asked Questions
VA vs watts for UPS?
VA = apparent power. Watts = real power. UPS is rated in VA; connected devices draw watts. Power factor = watts/VA (typically 0.6-0.9 for IT loads).
How much UPS runtime do I need?
Enough to gracefully shut down OR bridge to generator start (60-90 seconds). More runtime = bigger/more expensive UPS.
Extended runtime?
Add battery packs. Most line-interactive UPS support external battery modules. Enterprise UPS have scalable battery banks.