Impedance Calculator - AC Circuit Analysis

Calculate impedance, phase angle, and complex components for AC circuits. Free online tool for electrical engineering.

Inputs

Results

Enter resistance and reactance to calculate impedance

Impedance is the total opposition to AC current flow.

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How the Impedance Calculator Works

Z = √(R² + X²), φ = arctan(X/R)

Calculates total impedance from resistance and reactance components. Impedance is the AC equivalent of resistance, including the phase angle between voltage and current.

  1. 1

    Step 1

    Enter the resistance value (R) in ohms

  2. 2

    Step 2

    Enter the reactance value (X) in ohms

  3. 3

    Step 3

    Positive X = inductive, negative X = capacitive

  4. 4

    Step 4

    View impedance magnitude and phase angle

Use Cases

Analyzing AC circuit behavior

Matching impedances for maximum power transfer

Designing filters and tuned circuits

Calculating power factor from impedance

Tips

  • 1

    Impedance Z combines R and X vectorially

  • 2

    Phase angle shows current-voltage relationship

  • 3

    Inductive circuits: current lags voltage (positive angle)

  • 4

    Capacitive circuits: current leads voltage (negative angle)

Common Mistakes

  • Adding R and X directly instead of using vector sum

  • Confusing impedance with resistance (Z ≠ R for AC)

  • Forgetting reactance sign convention

  • Not considering frequency dependence of reactance

Frequently Asked Questions

What is the difference between impedance and resistance?
Resistance opposes DC and AC equally. Impedance includes resistance plus reactance (from inductors/capacitors). Z = R for purely resistive circuits; Z = √(R² + X²) otherwise.
Why does phase angle matter?
Phase angle determines power factor (cos φ). At 0°, all power is useful. At 90°, no real power is delivered - it just oscillates. Phase angle affects circuit efficiency.
How do I use impedance for power calculations?
Power = V²/Z × cos(φ) or I²Z × cos(φ). The cos(φ) term is the power factor. Only the resistive component of impedance dissipates real power.

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