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Resonant Circuit Calculator

Calculate LC tank circuit resonant frequency from inductance and capacitance. Q factor and impedance at resonance for RF design.

Use this result well

Inputs that matter
Inductance, Capacitance
Output to expect
LC Resonant Frequency
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Electrical Work

Reference & details

How it works

Resonant Frequency

Classic LC resonance formula. L in henries, C in farads, f in Hz. For μH and pF: f (MHz) = 1 ÷ (2π × √(L_μH × C_pF × 10⁻¹²))

f = 1 ÷ (2π × √(L × C))

Parallel LC Impedance at Resonance

At resonance, parallel LC impedance peaks. Q factor = R / XL determines selectivity and impedance magnitude.

Z = Q × XL (theoretical, limited by parasitic R)

Capacitor Reactance at Resonance

At resonance, inductive and capacitive reactances cancel. Either reactance value equals the impedance magnitude divided by Q.

XL = XC at resonance; XL = 2πfL

Updated: July 2026

Example Scenarios

L = 2.5 μH, C = 180 pF → resonance at 7.48 MHz — suitable for 40-meter band filter center frequency.

Verify external LC values don't pull crystal frequency. Load capacitance affects crystal resonance — use manufacturer load spec.

Calculate LC values to transform 50 ohm feed to 200 ohm antenna impedance at 14.2 MHz for L-network matching.

FAQ

Parallel or series combination of inductor and capacitor that resonates at f = 1/(2π√LC). Used in oscillators, filters, and antenna matching networks.

Formula requires henries and farads. Practically: microhenries (μH) and picofarads (pF) for RF. Convert: 1 μH = 10⁻⁶ H, 1 pF = 10⁻¹² F.

Quality factor measures selectivity — ratio of stored energy to dissipated energy per cycle. High Q = narrow bandwidth. Q = f / bandwidth (Hz).

Series LC: minimum impedance at resonance (short circuit ideally). Parallel LC: maximum impedance at resonance (open circuit ideally). Both resonate at same frequency.

Coil self-capacitance, capacitor ESR, and board parasitics shift actual resonance below calculated value. Build with 5% component tolerance and tune if needed.

About Resonant Circuit Calculator

LC tank circuits resonate at a frequency determined by inductance and capacitance values. Enter L in henries and C in farads (or common subunits μH and pF) to calculate resonant frequency, and estimate impedance characteristics at resonance.