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Series RLC Impedance

Z=R2+(XL−XC)2Z = \sqrt{R^{2} + (X_{L} - X_{C})^{2}}
sig figs

Worked example: 30 Ω with 80 Ω XL and 40 Ω XC → 50 Ω. Press Try an example to run it live, then adjust anything.

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Where Series RLC Impedance fits

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Phasor Sum of Two Series Impedances

See also

Series RL or RC Impedance: Both use impedance magnitude and resistance.Capacitive Reactance (X_C = 1/2πfC): Both use capacitive reactance.Inductive Reactance (X_L = 2πfL): Both use inductive reactance.Phasor Sum of Two Series Impedances: Both use impedance magnitude.555 Astable Frequency: Both use resistance.Current Divider: Both use resistance.
5 more relatedLED Series Resistor: Both use resistance.Q Factor of a Series Resonant Circuit: Both use resistance.Voltage Divider: Both use resistance.RC Cutoff Frequency: Both use resistance.RL Cutoff Frequency: Both use resistance.
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Series RLC Impedance explained

RXL − XCZ

Reactances are 90° out of phase with resistance and 180° out of phase with each other, so they subtract first and then join R by Pythagoras. With R = 30 Ω, XL = 80 Ω and XC = 40 Ω, the net reactance is 40 Ω and Z=302+402=50Z = \sqrt{30^2 + 40^2} = 50 Ω. Note that reactances can each be far larger than the total impedance: at resonance they cancel exactly and Z collapses to R alone, which is how a tuned circuit picks one station out of the air.

Because the square root discards sign, solving for a reactance has two answers; this brain returns the inductive-dominant branch (XL above XC), so subtract the root instead if you know the circuit is capacitive. The practical warning: never add reactances arithmetically to resistance. A 300 Ω coil in series with 400 Ω of resistance is 500 Ω, not 700 Ω, and a meter that reads otherwise is measuring DC.

Series RLC Impedance formula

Z=R2+(XL−XC)2Z = \sqrt{R^{2} + (X_{L} - X_{C})^{2}}
Where
  • ZZ= Impedance magnitude (Ω)
  • RR= Resistance (Ω)
  • XLX_{L}= Inductive reactance (Ω)
  • XCX_{C}= Capacitive reactance (Ω)
Revised 16 October 2026
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formula.expert. (2026, October 16). Series RLC Impedance Formula & Calculator. https://formula.expert/solvers/series-rlc-impedance

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