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UPS Load Calculator

Size a UPS for a connected load with headroom and power factor accounted for.

About UPS Load Calculator

UPS units are rated in kVA but loads are specified in watts, so power factor must be applied. Running above about 80 per cent of nameplate shortens both battery and electronics life. A UPS loaded above 90 per cent has no capacity for the inrush of a restarting load, which is when it is most likely to be needed.

Formula

UPS Load

UPS kVA = load ÷ power factor × (1 + headroom) ÷ maximum loading

maximum loading
UPS units are not run at nameplate continuously

Worked example

With the default values below, UPS Load Calculator returns UPS Rating Required of 5.208. Change any input above and every figure here is recalculated in your browser.

Inputs used

Connected loadminimum 0 W
3,000 W
Load power factoraccepts 0.1–1
0.9
Headroom for growthaccepts 0–100 %
25 %
Maximum continuous loadingaccepts 0–100 %
80 %

Results

UPS Rating Required
5.208 kVA
Load in Apparent Power
3.333 kVA
Nearest Standard UPS Size
6.0 kVA
Loading at That Size
55.6%
Spare Capacity
2,400.0 W

Step by step

  1. 1Values used
  2. 2UPS Load
  3. 3UPS Rating Required= 5.208 kVA
  4. 4Load in Apparent Power= 3.333 kVA
  5. 5Nearest Standard UPS Size= 6.0 kVA
  6. 6Loading at That Size= 55.6
  7. 7Spare Capacity= 2,400.0 W

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is UPS Load calculated?

UPS kVA = load ÷ power factor × (1 + headroom) ÷ maximum loading UPS units are rated in kVA but loads are specified in watts, so power factor must be applied. Running above about 80 per cent of nameplate shortens both battery and electronics life.

Why does UPS Load matter?

A UPS loaded above 90 per cent has no capacity for the inrush of a restarting load, which is when it is most likely to be needed.

What values do I need to enter?

This calculator takes 4 inputs: Connected load, Load power factor, Headroom for growth, Maximum continuous loading. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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