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UPS & Backup Power Calculators

UPS Runtime Calculator

How long a UPS will run your load, from battery capacity, voltage and inverter efficiency.

Enter values

Results update as you type.

Result

Runtime

2 h 2 min

Decimal hours
2.04
Usable energy
1.02 kWh
Battery total energy
2.4 kWh
Discharge current
24.51 A
Runtime at half load
4.08 hours

About the UPS Runtime Calculator

How long a UPS will run your load, from battery capacity, voltage and inverter efficiency.

Also known as: ups backup time, how long will ups last, inverter runtime calculator, battery backup time.

How to use this calculator

  1. Enter battery capacity, battery voltage, load, inverter efficiency and the other fields.
  2. The result updates instantly as you type — press Calculate (or Enter) at any time.
  3. Review the breakdown shown under the main result.
  4. Use Copy result or Share to save the answer or send a link with your inputs.

Formula

runtime = Ah × V × DoD × efficiency ÷ load

Worked example

Using the values pre-filled in the calculator above:

  • Battery capacity = 100 Ah
  • Battery voltage = 24 V
  • Load = 500 W
  • Inverter efficiency = 85 %
  • Usable depth of discharge = 50 %
  • Power factor = 1

the calculator returns:

  • Runtime: 2 h 2 min
  • Decimal hours: 2.04
  • Usable energy: 1.02 kWh
  • Battery total energy: 2.4 kWh