AC Power Calculator

Calculate real, apparent and reactive power for single-phase or balanced three-phase AC circuits

For three-phase calculations, enter line-to-line voltage and line current. This assumes a balanced load.

Your result will appear here.

About the AC Power Calculator

AC power calculations depend on voltage, current, phase and power factor. Unlike a simple DC circuit, volts multiplied by amps gives apparent power unless the load is purely resistive or power factor is 1.

This calculator helps distinguish watts, volt-amperes and three-phase relationships. Real equipment sizing should still follow nameplate ratings and electrical standards.

How to Use the AC Power Calculator

  1. Choose single-phase or three-phase mode.
  2. Enter voltage and current.
  3. Enter power factor when calculating real power.
  4. Calculate watts, VA or current as needed and verify whether voltage is line-to-line or line-to-neutral in the selected three-phase formula.

How the Calculation Works

For single-phase AC, apparent power S = VI and real power P = VI×PF.

For balanced three-phase systems using line-to-line voltage, S = √3 VI and P = √3 VI×PF. Reactive power and phase angle can be derived when the supported inputs provide them.

Worked example

AC Power Calculator Worked Example

400 V three-phase, 20 A, PF 0.85

Real power = √3×400×20×0.85 ≈ 11,778 W, or about 11.8 kW.

Result guide

Understanding Your AC Power Calculator Result

The result shows the steady-state electrical relationship under the selected phase and power-factor assumptions. Motors and other loads can draw much higher current during startup.

Before you rely on the answer

Assumptions and Limitations

  • Phase configuration is selected correctly.
  • Voltage definition matches the formula used.
  • Power factor reflects the actual load condition.

Practical tip

Using This Result in Practice

For equipment selection, use the manufacturer’s full-load and starting-current data rather than sizing from calculated real watts alone. Protection and conductor sizing involve additional requirements.

Related calculations

Useful Calculations to Continue With

For a broader volts-amps-watts relationship that also covers DC, use the Electrical Power Calculator.

If real and apparent power are known and power factor is the missing quantity, use the Power Factor Calculator.

Common questions

AC Power Calculator FAQ

What is the difference between kW and kVA?

kW is real power, while kVA is apparent power. They are related by power factor.

Why is √3 used in three-phase power?

It comes from the 120-degree phase relationship in a balanced three-phase system using line quantities.

Can I assume power factor equals 1?

Only for loads where that assumption is appropriate; many motors and electronic loads have lower or varying power factor.