Reactance and LC Resonance Calculator
The resonant frequency of an LC circuit is f0 = 1/(2*pi*sqrt(L*C)). At a given frequency f, inductive reactance is XL = 2*pi*f*L and capacitive reactance is XC = 1/(2*pi*f*C). Enter L, C or f to get the result in ohms or hertz.
Reactance / LC (follows the mode)
5.033 MHz
ω = 31620000 rad/s · XL = XC = 316.2 Ω
Ideal lossless values. Real parts deviate via inductor self-resonant frequency and DCR, capacitor ESR and ESL, and component tolerance.
FAQ
- What formula gives the resonant frequency of an LC circuit?
- It is the Thomson tuned-circuit equation: f0 = 1/(2*pi*sqrt(L*C)), with L in henries and C in farads. At resonance the reactances are equal: XL = XC = sqrt(L/C). We also show the angular frequency omega = 2*pi*f0 in rad/s.
- How do I compute XL and XC at a given frequency?
- Inductive reactance is XL = 2*pi*f*L (in ohms, phase +90 deg, voltage leads). Capacitive reactance is XC = 1/(2*pi*f*C) (in ohms, phase -90 deg, voltage lags). Every field is converted to SI units before the calculation runs.
- What are the Q factor and bandwidth outputs for?
- If you enter a series resistance R greater than 0 (coil DCR, capacitor ESR), we compute Q = (1/R)*sqrt(L/C) and the -3 dB bandwidth: BW = f0/Q = R/(2*pi*L). A higher Q means a narrower, more selective resonant peak.
- Why does my real circuit not resonate exactly at f0?
- The formulas assume ideal lossless parts. In practice the inductor self-resonant frequency (SRF), its DCR, the capacitor ESR and ESL, and component tolerances all shift f0. Above its SRF an inductor behaves capacitively. Leave margin and measure on the bench.
- Which units does the calculator accept?
- Inductance in pH, nH, uH, mH, H; capacitance in pF, nF, uF, mF, F; frequency in Hz, kHz, MHz, GHz. Everything is converted to SI units before computing, then outputs are auto-scaled for display (for example 5.033 MHz or 62.83 ohm).
A filter, tuned circuit or matching network that will not land on the right frequency? Book a free 30-min audit with our design office.
Built by AESTECHNO, an electronic design office in Montpellier, France. Over 10 years of experience in RF design, filtering and tuned circuits, with a 100% first-pass record on CE/FCC certification.