How to Use AC Power Calculator
The AC Power Calculator helps you find the active, apparent, and reactive power of any AC circuit in one step.
- Select phase type — Choose "Single-Phase" or "Three-Phase" at the top of the AC Power Calculator.
- Enter voltage (V) — Input the line-to-neutral voltage for single-phase, or line-to-line voltage for three-phase circuits.
- Enter current (A) — Input the RMS current in amperes.
- Enter power factor — Provide a value between 0 and 1 (e.g. 0.85 for a typical motor).
- Read results — The AC Power Calculator instantly outputs active power in W and kW, apparent power in VA and kVA, and reactive power in VAR and kVAR.
Formula & Theory — AC Power Calculator
The AC Power Calculator implements the standard AC power triangle formulas:
Single-phase:
Active Power: P = V × I × PF (W)
Apparent Power: S = V × I (VA)
Reactive Power: Q = V × I × sin(φ) (VAR)
Three-phase:
Active Power: P = √3 × V × I × PF (W)
Apparent Power: S = √3 × V × I (VA)
Reactive Power: Q = √3 × V × I × sin(φ)(VAR)
| Symbol | Meaning |
|---|---|
| V | RMS voltage (volts) |
| I | RMS current (amperes) |
| PF | Power factor (cos φ), 0 to 1 |
| sin(φ) | Computed as √(1 − PF²) |
| √3 | ≈ 1.732, three-phase constant |
Power Factor and Phase Angle
The AC Power Calculator derives sin(φ) automatically from the power factor you enter, using the identity sin(φ) = √(1 − cos²φ). This means you only need to know the power factor — no phase angle lookup required.
Use Cases for AC Power Calculator
The AC Power Calculator is used across a wide range of engineering and everyday electrical scenarios:
- Home appliance sizing — Use the AC Power Calculator to find the active power draw of air conditioners, refrigerators, or washing machines given their rated voltage, current, and power factor.
- Industrial motor analysis — Engineers use the AC Power Calculator to determine the reactive power demand of three-phase induction motors for power factor correction planning.
- Generator sizing — When specifying a backup generator, the AC Power Calculator helps match the apparent power (kVA) rating to connected loads.
- Electrical panel design — The AC Power Calculator supports load analysis for circuit breaker sizing and panel scheduling.
- Energy efficiency audits — By comparing active and apparent power, the AC Power Calculator reveals how much reactive power a facility consumes, enabling targeted power factor correction.
- Electronics education — Students use the AC Power Calculator to verify AC circuit theory and understand the relationship between P, Q, and S in the power triangle.