Electrical Power Calculator

DC and AC electrical power calculator with mode switching.

Calculate watts from voltage and current for DC and AC circuits. Switch between DC, AC single-phase, and AC three-phase modes.

Updated June 2026 · How this works

Voltage (V)

Current (A)

Power Factor

Phase Multiplier (√3)

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Worth knowing

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How It Works

The formula, explained simply

Electrical power is the rate at which energy is transferred. In DC circuits, power equals voltage times current. In AC circuits, the power factor accounts for the phase difference between voltage and current caused by reactive loads like motors and capacitors.

When To Use This

Right tool, right situation

Common Mistakes

Why results sometimes look wrong

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The Math

Worked examples and deeper derivation

DC: P = V × I

AC Single-Phase: P = V × I × PF

AC Three-Phase: P = V × I × PF × √3

Where PF (power factor) ranges from 0 to 1. Resistive loads have PF = 1.0.

DC circuit — 120V, 10A

V = 120V, I = 10A

P = V × I = 1,200 W

AC single-phase — 240V, 15A, PF 0.9

V = 240V, I = 15A, PF = 0.9

P = 240 × 15 × 0.9 = 3,240 W

AC three-phase — 415V, 20A, PF 0.85

V = 415V, I = 20A, PF = 0.85, phases = 1.732

P = 415 × 20 × 0.85 × 1.732 = 12,221 W

Common questions about electrical power

What is power factor?

Power factor is a number between 0 and 1 describing how efficiently electrical power is used. A power factor of 1.0 means all drawn power does useful work. Motors and fluorescent lights typically have power factors of 0.8 to 0.95.

When do I use three-phase calculation?

Three-phase power is standard in industrial settings and large commercial buildings. Use this mode when your system has three separate power lines, each offset by 120 degrees.

What is the difference between watts and volt-amps?

Watts measure real power — the work actually done. Volt-amps measure apparent power. The ratio between them is the power factor. For resistive loads they are equal.

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