Single-Phase Power Calculator

Compute real power (W), apparent power (VA), reactive power (VAR), power factor, voltage, and current for single-phase AC or DC.

How to Use

  1. Select Mode: AC (single-phase) or DC.
  2. Enter any two or more known values (common: V + A + PF for AC, V + A for DC).
  3. Pick the correct units (V/kV, A/mA, W/kW, etc.).
  4. Open Show Work for formulas and step-by-step calculations.
Power Lab View
Instant readout of W, VA, VAR, PF, and key electrical values.
W
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VA
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VAR
—
PF
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Load: —
Source V Load (P / PF) W / VA / VAR I (A) PF AC mode uses PF for real power. DC mode treats PF = 1 and VAR = 0.
Inputs & Settings
Enter what you know. The calculator will compute the rest.
AC uses power factor. DC assumes PF=1 and VAR=0.
Common: 50Hz, 60Hz (used for reference only unless JS adds impedance features).
Examples: 120V, 230V, 277V
Examples: 1.5A, 10A, 30A
Range: 0 to 1. Resistive loads ~1. Motors often 0.7–0.95.
Real power consumed (heat/work): W or kW
Transformer/utility loading: VA or kVA
Reactive component (magnetizing): VAR or kVAR
Show Work (step-by-step)
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Work is shown using base units (V, A, W, VA, VAR) for clarity.

Formulas

Single-phase power relationships (AC uses PF; DC behaves like PF = 1).

  • Apparent power: S = V × I (VA)
  • Real power (AC): P = V × I × PF (W)
  • Real power (DC): P = V × I (W)
  • Reactive power (AC): Q = √(S² − P²) (VAR)
  • Power factor: PF = P / S
Where V = volts (RMS for AC), I = amps (RMS for AC), P = watts, S = volt-amps, Q = vars.

FAQ

What’s the difference between W and VA?

VA is apparent power (S) and represents total electrical loading. W is real power (P) and represents usable work/heat. They differ when PF < 1.

When is VAR used?

VAR (Q) appears in AC systems with inductive/capacitive loads (motors, transformers). It’s linked to magnetic field energy exchange.

What should PF be for DC?

For ideal DC loads, PF is effectively 1 and reactive power is 0.

Tool Info

Last updated:

Updates may include UI improvements, added unit support, and edge-case handling.