Impedance Calculator

Step-by-Step Guide

1. 1Enter Resistance (R): Input the circuit's resistance value, choosing Ω, kΩ, or MΩ.
2. 2Enter Inductive Reactance (XL): Input inductive reactance, calculated as XL = 2πfL if not already known.
3. 3Enter Capacitive Reactance (XC): Input capacitive reactance, calculated as XC = 1/(2πfC) if not already known.
4. 4Read Impedance and Phase Angle: View total impedance (Z), net reactance, and the phase angle between voltage and current.
5. 5Check the Circuit Classification: See whether the circuit is inductive, capacitive, resistive, or resonant.

What This Calculator Provides

• ✓Real-time calculation as you type
• ✓Total impedance (Z) and net reactance
• ✓Phase angle between voltage and current
• ✓Automatic circuit type classification
• ✓Full step-by-step derivation
• ✓Six built-in circuit presets
• ✓Calculation history
• ✓Export calculation as a text file
• ✓No signup required

Pro Tips

• 💡Calculate XL and XC at the specific frequency you care about before entering them here — both are frequency-dependent, so impedance at 60Hz will be very different from impedance at 1kHz for the exact same components.
• 💡Use the phase angle sign as a quick diagnostic: positive means inductive (voltage leads), negative means capacitive (current leads), and near-zero means the circuit is close to resonance at that frequency.
• 💡For speaker and amplifier matching, remember that rated impedance (like 8Ω) is a nominal figure — actual impedance varies with frequency due to the voice coil's inductance, so a speaker's true impedance curve dips and rises across its frequency range.
• 💡When troubleshooting, compare the calculated impedance and phase angle against oscilloscope measurements of voltage and current phase difference — a mismatch points to an unaccounted-for component or incorrect reactance values.
• 💡Use the built-in presets to build intuition for how R, XL, and XC interact before switching to your own real circuit's values — the resonant circuit preset is especially useful for seeing what zero net reactance looks like.

Common Mistakes to Avoid

• ✕Adding R, XL, and XC arithmetically instead of using the vector (Pythagorean) combination. Impedance is Z = √(R² + (XL-XC)²), not R + XL - XC — the phase relationship between resistance and reactance means they can't simply be summed.
• ✕Forgetting that XL and XC change with frequency. A circuit calculated as resonant at 1kHz will not be resonant at 10kHz using the same component values, since both XL and XC scale differently with frequency.
• ✕Confusing net reactance sign convention. XL - XC positive means inductive; if you accidentally reverse the subtraction (XC - XL), the phase angle sign flips, making an inductive circuit look capacitive in your result.
• ✕Ignoring that impedance is frequency-specific data. Reporting a single impedance value without noting the frequency it was calculated at makes the number meaningless for anyone trying to reproduce or verify the calculation later.
• ✕Using DC resistance measurements as if they equal impedance in an AC circuit. A component's DC resistance and its AC impedance at a given frequency can differ significantly once reactance is included.