kVA Calculator

Use this kVA calculator to find the value of apparent power from the operating voltage and current in a system.

Apparent power3.1579 kVA3.1579 kVA — what the supply and cabling must carry, regardless of power factor

Current13.73 Asingle-phase AC at 230 V, as entered

Real power3 kW4.0231 hp equivalent

Reactive power986.0523 VARcirculates without doing work, yet still heats the cable

Power factor0.95cos of the phase angle, 18.19°

Current at unity power factor13.0435 A686.4989 mA less — correcting power factor reduces current for the same useful work

Same load on three-phase7.927 Aper line, at the same line voltage

Breaker at 125% of the load17.16 Acontinuous loads are conventionally sized this way, then rounded up to the next standard rating

Energy a day12 kWh

Cost a day3.6

Cost a year1,314note that most tariffs bill real energy in kWh, so a poor power factor costs a domestic customer nothing directly — industrial tariffs often penalise it

The formula

P = VI for DC; VI·pf single-phase; √3·V_L·I_L·pf three-phase

Three supplies, three different answers

The current a load draws for a given real power depends on the supply. DC is simply P/V. Single-phase AC divides by the power factor as well, because voltage and current are out of step and not all the flowing current does work. Three-phase divides additionally by √3, since the three line voltages are 120° apart. Quoting a current without saying which convention was used is how cables get undersized.

Apparent power in VA is what the cabling and the transformer must actually carry; real power in watts is what does useful work. The gap between them is reactive power, which circulates without doing anything useful and still heats the conductors. That is why transformers and generators are rated in VA rather than watts.

A motor's horsepower rating is its shaft output, not its electrical input. A 90%-efficient 5 hp motor draws about 4.1 kW, not 3.7 kW, and sizing the supply from the nameplate horsepower without dividing by efficiency undersizes it by exactly the loss.

On power factor and bills: domestic meters record real energy in kWh, so a poor power factor costs a household nothing directly. Industrial tariffs often charge for kVA or penalise low power factor, because the utility has to build for the apparent power.