AC Wattage Calculator

Compute active (P), reactive (Q), and apparent (S) power for single‑phase and three‑phase AC systems. Real‑time power triangle visualization.

Power Formulas: Single‑phase: P = V·I·PF, Q = V·I·sin(φ), S = V·I. Three‑phase (balanced): P = √3·VL·IL·PF, S = √3·VL·IL.

Home appliance (120V, 5A, 0.8 lag)
Industrial motor (480V, 10A, 0.85 lag)
Resistive heater (240V, 2A, PF=1)
Capacitive load (208V, 3A, 0.95 lead)
Three‑phase motor (400V, 5A, 0.78 lag)
Computing...

Understanding AC Power

In alternating current (AC) circuits, power is divided into three components: active power (P) measured in watts (W) that does useful work, reactive power (Q) in volt‑amperes reactive (VAR) that sustains magnetic and electric fields, and apparent power (S) in volt‑amperes (VA) which is the product of RMS voltage and current.

Key Relationships:

P = S · cos φ    Q = S · sin φ    S = √(P² + Q²)

Power factor PF = cos φ = P / S (0 ≤ PF ≤ 1)

For three‑phase balanced systems (line values): S = √3 · VL · IL

Power Triangle & Phase Angle

The power triangle visually represents the relationship between P, Q, and S. The angle φ between apparent power (hypotenuse) and active power (adjacent) is the phase shift between voltage and current. A lagging power factor (inductive load) means current lags voltage (positive Q), while a leading PF (capacitive load) means current leads voltage (negative Q).

Why Power Factor Matters

  • Low PF increases current for the same real power, causing higher losses and requiring larger conductors.
  • Utilities often charge penalties for low power factor.
  • Power factor correction (adding capacitors) reduces reactive power and improves efficiency.

Calculator Features:

  • Real‑time calculation for single‑phase and three‑phase systems.
  • Power triangle drawn dynamically based on P and Q (with sign).
  • Preset examples for common loads.
  • Includes optional frequency for reference.

Frequently Asked Questions

Active power (P) performs actual work (heat, motion). Reactive power (Q) is stored and returned by inductors/capacitors. Apparent power (S) is the total power supplied by the source. They are related by the power triangle.

Negative reactive power indicates a capacitive load (current leads voltage). In the power triangle, Q is drawn downward (opposite direction of inductive Q).

This version assumes balanced loads. For unbalanced systems, you would need to calculate each phase separately and sum the powers.