AC Power Calculator
Calculate active, apparent and reactive power for single-phase and three-phase AC circuits.
power
AC
single-phase
three-phase
kW
kVA
power factor
Input values
⚙
Enter values and click Calculate to see results here.
Formula
P = V × I × pf (single phase)
P = √3 × V × I × pf (three phase)
Worked Example
Given: A three-phase motor draws 12 A at 400 V with a power factor of 0.85.
Step 1: P = √3 × 400 × 12 × 0.85 = 7,056 W = 7.06 kW
Step 2: S = √3 × 400 × 12 = 8,314 VA = 8.31 kVA
Step 3: Q = √3 × 400 × 12 × sin(arccos(0.85)) = 4.40 kVAR
The motor requires a 10 A breaker minimum and the cable must be rated for at least 10 A.
Engineering Notes
- Active power (kW) is the real power consumed. Size generators, cables, and breakers based on this.
- Apparent power (kVA) is what the transformer and UPS see. Always check the kVA rating of your supply equipment.
- Reactive power (kVAR) is wasted energy circulating between source and load. Power factor correction capacitors reduce this.
- Power factor: Most motors run 0.8–0.9. If below 0.8, investigate — it wastes energy and may cause utility penalties.
- PLC analog inputs: Use this calculator to verify that power measurements from CT/PT sensors are correct.
References
- IEC 60034-1 — Rating of rotating electrical machines
- IEC 61439-1 — Low-voltage switchgear and controlgear assemblies