Find where an LC circuit resonates
An inductor's reactance rises with frequency, a capacitor's falls. Where they cross is the resonant frequency — compute it before you wind a coil.
Tools used in this guide
The job
Every filter and tuned circuit boils down to XL = 2πfL climbing and XC = 1/(2πfC) falling. Series resonance sits where they are equal: f = 1/(2π√LC). The tool evaluates all of these plus the net reactance at any frequency.
Frequency in, reactance out
Enter the frequency plus the inductance and capacitance with units — the tool reports XL, XC, their difference, and where the pair resonates.
Worked example
At 50 Hz, a 0.1 H inductor shows XL ≈ 31.4 Ω — too small to isolate much; at 1 MHz a 100 pF capacitor shows XC ≈ 1,592 Ω. Pair 10 µH with 100 pF and they resonate at 5.03 MHz — a classic shortwave band trap.
Scope
Frequency 0.01 Hz–1 THz, L 1 pH–1 kH, C 1 fF–1 kF. Ideal components only: ESR, self-capacitance, and tolerance shift the real resonance — expect to trim.