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Impedance calculator (RLC)

Compute the impedance of a series or parallel RLC circuit at any frequency. From R, L, C and f it returns the inductive and capacitive reactances, the impedance magnitude |Z|, the phase angle and the resonant frequency where the reactances cancel.

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Need Impedance magnitude |Z|, Phase angle, Inductive reactance XL, Capacitive reactance XC, Resonant frequency f₀, Circuit behaviour? The Impedance calculator (RLC) derives it from Circuit topology, Resistance R, R unit, Inductance L, L unit, Capacitance C, C unit, Frequency f, f unit in one step. For instance, with Circuit topology = Series RLC, Resistance R = 100, R unit = Ω, Inductance L = 50, L unit = H, Capacitance C = 10, C unit = F, Frequency f = 1 and f unit = Hz it returns Impedance magnitude |Z| = 329.676 Ω, Phase angle = 72.342 ° and Inductive reactance XL = 314.159 Ω.

How to use it

  1. Enter your values: Circuit topology, Resistance R, R unit, Inductance L, L unit, Capacitance C, C unit, Frequency f, f unit.
  2. Read the result instantly: Impedance magnitude |Z|, Phase angle, Inductive reactance XL, Capacitive reactance XC, Resonant frequency f₀, Circuit behaviour.

Frequently asked questions

What does the Impedance calculator (RLC) actually compute?

It takes Circuit topology, Resistance R, R unit, Inductance L, L unit, Capacitance C, C unit, Frequency f and f unit and derives Impedance magnitude |Z|, Phase angle, Inductive reactance XL, Capacitive reactance XC, Resonant frequency f₀ and Circuit behaviour from them. The calculation is live as you type, so the result updates on every change.

What information do I need to provide?

9 values: Circuit topology, Resistance R, R unit, Inductance L, L unit, Capacitance C, C unit, Frequency f and f unit. Nothing else is required — no account, no file upload.

Can you show a worked example?

With Circuit topology = Series RLC, Resistance R = 100, R unit = Ω, Inductance L = 50, L unit = H, Capacitance C = 10, C unit = F, Frequency f = 1 and f unit = Hz, the calculator returns Impedance magnitude |Z| = 329.676 Ω, Phase angle = 72.342 ° and Inductive reactance XL = 314.159 Ω. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

What happens if I enter larger values?

It moves a lot. Using Circuit topology = Parallel RLC, Resistance R = 200, R unit = kΩ, Inductance L = 100, L unit = mH, Capacitance C = 20, C unit = mF, Frequency f = 2 and f unit = kHz instead, Impedance magnitude |Z| goes from 329.676 Ω to 0.004 Ω — which is why it is worth testing a few scenarios rather than trusting a single figure.

Which “Circuit topology” option should I choose?

You can pick between « Series RLC » and « Parallel RLC ». Each one changes what the calculator works out, so switch and compare — the default is « Series RLC ».

When would I actually use this?

At the bench: sizing a resistor for an LED, reading a colour band, working out a divider ratio, and checking a part will not cook.

What is the most common mistake?

Choosing a resistance and forgetting the power rating. A value that is electrically right will still burn if the package cannot dissipate what passes through it — check the watts as well as the ohms.

What is the difference between the Impedance calculator (RLC) and the Inductive reactance calculator?

This one returns Impedance magnitude |Z| and Phase angle; the Inductive reactance calculator returns Frequency and Inductance. That is the whole difference — open the one whose figure you need.

Is there a tool for the next step?

555 timer calculator (astable & monostable) is the closest one after this: Design a 555 timer circuit in either mode. In astable mode, R1, R2 and C set the output frequency, high and low times and duty cycle; in monostable mode, R1 and C set the one-shot pulse width. The classic hobbyist chip, sized in seconds.

What else is worth having open alongside it?

PCB trace width calculator (IPC-2221) and Antenna length calculator — they come up in the same task often enough to be worth a second tab.

Further reading

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ExplainerResistors in Series and in Parallel: The Formulas, and the Three Things They Do Not Tell YouSeries adds, parallel adds reciprocals — that part is easy. The parts that catch people: which member dominates the answer, why two 5 % resistors in parallel are still 5 %, and why the smallest resistor in a parallel pair takes the largest share of the power.ExplainerThe Voltage Divider: The Formula Is Trivial, the Assumption Behind It Is NotVout = Vin·R2/(R1+R2) is only true when nothing is connected to the output. Draw current and the voltage collapses, by an amount that follows one exact law. Here is that law, the ten-times rule checked against it, and why a lower-resistance divider costs you power forever.How-toHow to Calculate an LED Series ResistorSize the series resistor for any LED with one formula: R = (Vs − Vf) / I. Follow the steps, see a worked 5 V example, and pick the right resistor.ExplainerWhat Is Ohm's Law? V = I × R Explained SimplyOhm's law links voltage, current, and resistance with one equation: V = I × R. Learn the triangle trick and see worked examples.ComparisonSolar Panels: the Self-Consumption Rate Decides the PaybackSince June 2026 a French rooftop is paid 1.1 cents for an exported kilowatt-hour and avoids 25.61 cents by consuming the same one. That ratio of 23 to 1 makes the self-consumption rate — the variable almost every quote omits — worth more than the amount of sun falling on the roof.ComparisonHeat Pump or Gas Boiler: the SCOP Your Local Prices DemandBefore any grant, the price of electricity divided by the price of gas sets a seasonal efficiency the heat pump must beat just to break even on running cost. In late 2025 that number was 1.53 in Portugal and 2.79 in Germany — and on old radiators a German heat pump can cost more to run than the boiler it replaced.