AC Power Calculator
Enter voltage, current and power factor for a single- or three-phase circuit to see real power in kW, apparent power in kVA and reactive power in kVAR, plus the phase angle.
This AC power calculator turns voltage, current and power factor into real, reactive and apparent power. Real power (kW) is what does the work, apparent power (kVA) is what the supply has to carry, and reactive power (kVAR) is the part swapped back and forth by motors and transformers. It doubles as a power factor calculator and a kVA to kW calculator, and it handles both single-phase and balanced three-phase loads. Enter volts and amps, or flip it around and solve the current from a known kW load.
AC circuit
Power factor is the ratio of real to apparent power. Resistive heaters sit near 1.0; motors and transformers run lower, often 0.7–0.9.
Real power
1.84 kW
1,840 W · single-phase at PF 0.8
- Apparent power
- 2.3 kVA
- Reactive power
- 1.38 kVAR
- Power factor
- 0.8
- Phase angle
- 36.9°
Apparent power (kVA) is the total the supply must carry: V × I, and √3 × V × I for a balanced three-phase load. Real power (kW) is the useful part, S × PF, and the reactive part (kVAR) is what shuttles back and forth in the magnetic and electric fields.
This assumes a balanced, sinusoidal load and treats power factor as purely displacement. Harmonics, unbalance and inrush shift the real figures, so size cables, breakers and generators from measured values or the equipment nameplate.
How it works
- 1
Pick phase and inputs
Choose single- or three-phase, then enter voltage and current, or switch to the known-kW mode to solve back for the line current.
- 2
Set the power factor
Drag the power factor from 0 to 1. Resistive heaters sit near 1.0; motors and fluorescent gear run lower, around 0.7 to 0.9.
- 3
Read the power triangle
See real power in kW, apparent power in kVA, reactive power in kVAR and the phase angle, then copy the result.
Instant & 100% private — nothing is uploaded
Every calculation runs locally in your browser. The income, balances and goals you enter stay on your own device and are never sent to a server — nothing is stored, logged or shared.
Frequently asked questions
- What is the difference between kW and kVA?
- kW is real power, the part that actually does work and turns into heat, light or motion. kVA is apparent power, the total the wiring and supply must carry. They are equal only at a power factor of 1; below that, kVA is always larger than kW.
- How do I convert kVA to kW?
- Multiply the apparent power in kVA by the power factor: kW = kVA × PF. So 10 kVA at a power factor of 0.8 is 8 kW. This tool does that step and also shows the reactive kVAR.
- How does the three-phase calculation differ?
- For a balanced three-phase load using line-to-line voltage and line current, apparent power is √3 × V × I, about 1.732 times the single-phase figure. Real and reactive power then follow from the power factor the same way.
- What is reactive power in kVAR?
- Reactive power is the energy that shuttles back and forth in the magnetic and electric fields of motors, transformers and capacitors without doing net work. It is S × sin(acos(PF)), and correcting a low power factor is what shrinks it.
- Can I find the current from a known kW rating?
- Yes. Switch to the known-kW mode, enter the real power and power factor, and the calculator back-solves the line current from S = V × I (or √3 × V × I for three-phase), which is handy for sizing cables and breakers.
- What power factor should I use?
- Use the value on the equipment nameplate if you have it. Otherwise, purely resistive loads are near 1.0, induction motors under load are roughly 0.8 to 0.9, and lightly loaded motors or old ballasts can drop to 0.5 to 0.7.
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