About

Correctly sizing power distribution equipment requires distinguishing between apparent power and real power. Transformers and generators are typically rated in Volt-Amperes (VA) or kilovolt-Amperes (kVA), representing the total capacity irrespective of efficiency. However, the actual work performed by motors, heaters, and servers is measured in Kilowatts (kW). The discrepancy stems from the Power Factor, a measure of efficiency determined by phase shifts between voltage and current.

This tool bridges the gap for electrical engineers and facility managers planning load requirements. Using an incorrect conversion leads to undersized transformers (risk of overheating) or oversized infrastructure (unnecessary capital expenditure). The calculation accounts for the scalar difference between total power flow and usable power, defined by the efficiency of the connected load.

Formulas

The relationship between Real Power (P), Apparent Power (S), and Power Factor (PF) is derived from the power triangle. The conversion formula depends on the input unit scaling.

VA to kW:

VA × PF1000 = kW

kVA to kW:

kVA × PF = kW

kW to kVA (Reverse):

kWPF = kVA

Where PF is a dimensionless number between 0 and 1.

Reference Data

Load Type	Typical Power Factor PF	Equation	Notes
Resistive Load (Heaters)	1.0	kW ≈ kVA	Unity power factor. No phase shift.
Induction Motor (Full Load)	0.85 to 0.90	kW < kVA	Standard industrial motor efficiency.
Induction Motor (No Load)	0.10 to 0.30	kW ≪ kVA	High reactive power demand.
Arc Welding	0.35 to 0.55	Variable	Requires significant correction capacitors.
LED Lighting (Driver)	0.90 to 0.95	Electronics	Modern drivers have correction built-in.
Fluorescent (Magnetic Ballast)	0.40 to 0.60	Legacy	Highly inductive.
Server / IT Equipment	0.95 to 0.99	PSU	Active PFC is standard in data centers.
Air Compressor	0.75 to 0.85	Motor	Varies by loading cycle.
CNC Machines	0.65 to 0.80	Complex	Servos plus spindle loads.

Frequently Asked Questions

Transformers are limited by current (Amps) and insulation breakdown (Volts), not by the work performed (Watts). A transformer must handle the total current, including reactive current that doesn"t perform work but creates heat. Rating in kVA ensures the equipment can handle the total electrical load regardless of the Power Factor.

Not directly. Residential meters typically charge for kW-hours (Real Power). However, industrial tariffs often include penalties for a low Power Factor (excessive kVA demand relative to kW). While the calculation shows usable power, improving the Power Factor at the source is required to reduce utility surcharges.

A Power Factor of 0 implies a purely reactive load (like a perfect inductor or capacitor) where no real work is done. In this theoretical scenario, kW would be 0 regardless of the VA input. In practice, all equipment has some resistance, so PF is rarely exactly 0.

No. Since the Power Factor cosine theta cannot exceed 1.0, Real Power (kW) is always less than or equal to Apparent Power (kVA). If kW exceeds kVA, calculation inputs are incorrect or the system involves active power generation pushing back into the grid.