Apparent Power Calculator
Calculate apparent power in volt-amperes and the capacity it demands from supply equipment.
About Apparent Power Calculator
Equipment is rated in kVA because it must carry the full current regardless of phase angle. At a power factor of 0.8, a fifth of the supply capacity is tied up carrying reactive current that does no work. A generator rated 100 kVA delivers only 80 kW at 0.8 power factor, which is the most common sizing mistake in standby power.
Formula
Apparent Power
S = P ÷ power factor; line current = S ÷ V for single phase, S ÷ (√3 V) for three phase
- kVA
- The rating that transformers, cables and generators are sized on
Worked example
With the default values below, Apparent Power Calculator returns Apparent Power of 10.0000. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Real powerminimum 0 W
- 8,000 W
- Power factoraccepts 0.01–1
- 0.8
- Supply voltageminimum 1 V
- 400 V
- Phasesone of Single phase, Three phase
- Three phase
Results
- Apparent Power
- 10.0000 kVA
- Apparent Power
- 10,000.00 VA
- Line Current
- 14.434 A
- Reactive Power
- 6.0000 kVAR
- Supply Capacity Not Doing Useful Work
- 20.00%
Step by step
- 1Values used
- 2Apparent Power
- 3Apparent Power= 10.0000 kVA
- 4Apparent Power= 10,000.00 VA
- 5Line Current= 14.434 A
- 6Reactive Power= 6.0000 kVAR
- 7Supply Capacity Not Doing Useful Work= 20.00
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, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 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 Apparent Power calculated?
S = P ÷ power factor; line current = S ÷ V for single phase, S ÷ (√3 V) for three phase Equipment is rated in kVA because it must carry the full current regardless of phase angle. At a power factor of 0.8, a fifth of the supply capacity is tied up carrying reactive current that does no work.
Why does Apparent Power matter?
A generator rated 100 kVA delivers only 80 kW at 0.8 power factor, which is the most common sizing mistake in standby power.
What values do I need to enter?
This calculator takes 4 inputs: Real power, Power factor, Supply voltage, Phases. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.