AC Power Calculator

Calculate real power (W), apparent power (VA), reactive power (VAR), power factor, and phase angle for single-phase or three-phase AC circuits.

How to Use

  1. Select Single-phase or Three-phase.
  2. Enter RMS voltage and RMS current (or enter any two power values if supported by the tool mode).
  3. Enter Power Factor (PF) to compute real/reactive power, or switch PF mode to “Angle” if you prefer degrees.
  4. Open Show Work to see formulas and steps in base units.
Inputs & Settings
RMS values are assumed. Tool updates instantly in the browser.
Three-phase uses √3 × V × I × PF (line-to-line voltage assumed).
Examples: 120V, 240V, 208V, 230V, 480V
Examples: 0.5A, 10A, 32A, 100A
PF = cos(φ). Leading/lagging selection affects VAR sign only.
Valid range: 0 to 1 (typical motors: 0.7–0.95).
Angle φ in degrees. PF = cos(φ).
Does not change magnitudes, only the sign of reactive power.
Auto chooses the cleanest unit display.
Results
Computed from RMS inputs. Show Work uses base units.
Real Power (P)
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Apparent Power (S)
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Reactive Power (Q)
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Power Factor
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Phase Angle (φ)
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Notes
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Show Work (step-by-step)
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Work is shown in base units (V, A, W, VA, VAR) for clarity and consistency.

Reference

  • Apparent power: S = V × I (single-phase), S = √3 × V × I (three-phase)
  • Real power: P = S × PF
  • Reactive power: Q = S × sin(φ)
  • Power factor: PF = cos(φ)

Assumptions: RMS quantities, sinusoidal steady-state, balanced load for three-phase, and voltage in three-phase mode is line-to-line.

FAQ

Why doesn’t W equal VA?

Because reactive components (inductors/capacitors) shift current vs voltage. VA is total “supply burden,” W is real work/heat.

What’s the difference between leading and lagging?

Lagging indicates inductive loads (motors), leading indicates capacitive behavior. This tool uses that choice to set the sign of VAR.

Three-phase: why √3?

In balanced three-phase systems, line-to-line voltage and phase relationships produce the √3 factor in total power formulas.

Tool Info

Last updated:

Updates may include additional input modes, validation edge-cases, and export helpers.