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Calculator Tools
UPS & Backup Power Calculators

UPS Size Calculator

UPS VA and watt rating for your equipment, with headroom and the battery needed for runtime.

Enter values

Results update as you type.

Result

UPS rating

1,000 VA

Required VA
937.5
Required watts
750 W
Battery capacity needed
36.8 Ah
Battery energy needed
0.8824 kWh
100 Ah batteries
1

About the UPS Size Calculator

UPS VA and watt rating for your equipment, with headroom and the battery needed for runtime.

Also known as: va rating calculator, what size ups do i need, ups sizing, inverter va calculator.

How to use this calculator

  1. Enter total connected load, power factor, growth headroom, runtime needed 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

VA = watts ÷ power factor · battery Ah = Wh ÷ voltage

Worked example

Using the values pre-filled in the calculator above:

  • Total connected load = 600 W
  • Power factor = 0.8
  • Growth headroom = 25 %
  • Runtime needed = 30 min
  • Battery voltage = 24 V
  • Usable depth of discharge = 50 %

the calculator returns:

  • UPS rating: 1,000 VA
  • Required VA: 937.5
  • Required watts: 750 W
  • Battery capacity needed: 36.8 Ah