Inductor/Capacitor Reactance & Resonance
Reactance of an inductor and capacitor at a given frequency, plus the LC resonant frequency.
Worked example
Input: Frequency 10 MHz, Inductance L 100 nH, Capacitance C 100 pF
Result: Inductive reactance X_L 6.28319 Ω, Capacitive reactance X_C 159.155 Ω, LC resonant frequency 50.3292 MHz
Result: Inductive reactance X_L 6.28319 Ω, Capacitive reactance X_C 159.155 Ω, LC resonant frequency 50.3292 MHz
Formula
X_L = 2π·f·L
X_C = 1 / (2π·f·C)
f₀ = 1 / (2π·√(LC))
How it works
X_L = 2πfL grows with frequency while X_C = 1/(2πfC) falls. This is the basis for choosing decoupling capacitors, estimating ferrite/choke impedance and predicting resonances.
Practical tipReal parts have parasitic inductance and capacitance, so above the self-resonant frequency (SRF) their behaviour flips. A capacitor acts like an inductor above its SRF, so check the SRF when choosing the decoupling band.
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Results and summaries are for reference. For certification and test reports use the latest official standard text and calibrated instrument data. Last updated: 2026-10-10