Calculate capacitive reactance, inductive reactance, LC resonant frequency, and optional series RLC impedance context at a selected frequency.
Inputs and tolerances
Calculate reactance, resonance, and inverse component targets with tolerance ranges.
Use analysis mode for series RLC impedance and phase. Use inverse modes when the target is a component value or resonant frequency.
Reactance and resonance results
The ideal series LC branch is net capacitive at this frequency.
Frequency100kHzRange: 98k to 102k Hz
Angular frequency628.3krad/sRange: 615.8k to 640.9k rad/s
Capacitance100nFRange: 90n to 110n F
Inductance10µHRange: 8µ to 12µ H
Capacitive reactance magnitude15.92ohmRange: 14.18 to 18.04 ohm
Inductive reactance6.283ohmRange: 4.926 to 7.691 ohm
LC resonant frequency159.2kHzRange: 138.5k to 187.6k Hz
Net series reactance-j9.632ohmRange: -13.12 to -6.494 ohm
Series impedance magnitude13.88ohmRange: 11.51 to 16.8 ohm
Series phase angle-43.93degRange: -54.09 to -31.74 deg
Series Q estimate1Range: 812.2m to 1.215
Use this calculator when the question is frequency-domain behaviour, not equivalent-value reduction. It reports tolerance-aware reactance, resonance, impedance, and inverse component targets.
When inductive and capacitive reactance magnitudes match, the ideal series LC reactance approaches zero and real resistance controls the branch.
Series impedance
Add series resistance to estimate impedance magnitude, phase angle, and a first-pass Q value.
Choose RLC analysis, solve capacitance from a capacitive-reactance target, solve inductance from an inductive-reactance target, or solve one value in the ideal resonance relationship. Inputs support percentage tolerance, explicit input ranges, and engineering notation such as 100k, 100n, 10u, and 15.9.
Reactance
Analyse or solve component reactance
Use the analysis workflow for series impedance and phase, or solve C and L directly from target reactance at a selected frequency.
Resonance
Solve resonance values
Use the LC resonance workflows when two of frequency, inductance, and capacitance are known and the third is the design target.
The model assumes ideal lumped capacitance and inductance at one frequency. It does not include ESR, ESL, DCR, dielectric loss, skin effect, layout parasitics, source impedance, or load impedance.
Core equations
RLC frequency-domain model
Capacitive reactance
Capacitor reactance magnitude falls as frequency or capacitance rises.
Inductive reactance
Inductor reactance rises as frequency or inductance rises.
Ideal LC resonance
The ideal undamped resonant frequency for the selected L-C pair.
Series net reactance
Positive values are net inductive; negative values are net capacitive.
Series impedance magnitude
The ideal magnitude when a real series resistance is supplied.
Phase angle
The ideal series branch angle from the real resistance and net reactance.
Variables and units
f: Frequency
Unit: Hz
The AC frequency where reactance is evaluated.
C: Capacitance
Unit: F
The ideal capacitance used for capacitive reactance and resonance.
L: Inductance
Unit: H
The ideal inductance used for inductive reactance and resonance.
R: Series resistance
Unit: ohm
The series resistance required for the analysis workflow to calculate impedance magnitude, phase angle, and Q factor.
XC: Capacitive reactance
Unit: ohm
The magnitude of ideal capacitor reactance at the selected frequency.
XL: Inductive reactance
Unit: ohm
The ideal inductor reactance at the selected frequency.
f0: Resonant frequency
Unit: Hz
The ideal undamped frequency where inductive and capacitive reactance magnitudes match.
|Z|: Impedance magnitude
Unit: ohm
The magnitude of the ideal series branch impedance when resistance is included.
Model boundary
This is a first-pass ideal calculation. Real capacitors and inductors change with frequency, bias, temperature, package, winding construction, mounting geometry, and PCB layout.
This example checks a 100kHz branch with 100nF, 10uH, and 10 ohm series resistance.
Worked example
100kHz series RLC branch
At 100kHz, the capacitor reactance is larger than the inductor reactance, so the ideal branch is net capacitive.
Inputs
Design question
What are XC, XL, resonance, and series impedance for 100nF, 10uH, and 10 ohm at 100kHz?
f
100kHz
C
100nF
L
10uH
Equation and substitution
Reactance
Resonance
Series branch
The branch is net capacitive.
With 10 ohm R
Ideal reactance numbers are useful for planning, but they do not certify real circuit behaviour.
Parasitics shift the answer
Capacitor ESR and ESL, inductor DCR and inter-winding capacitance, and PCB loop inductance can dominate near high frequency or resonance.
Ratings still matter
Check capacitor voltage bias, ripple current, dielectric loss, inductor saturation current, current heating, and temperature range.
The circuit around it matters
Source impedance, load impedance, damping, and measurement fixture parasitics can move the observed response away from the ideal branch result.
Design follow-up
Next engineering checks
Use these follow-up checks before turning the calculated value into a component choice, layout decision, or production limit.
Check real component limits
Compare capacitor ESR, ESL, voltage bias, dielectric loss, inductor DCR, saturation current, and self-resonant frequency against the operating band.
