Resonant Frequency Calculator

Enter values for a series or parallel LC or RLC circuit. Solve for frequency, inductance, or capacitance, and get bandwidth and Q.

Free to useNo sign-up requiredUpdated Mar 2026

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About Resonant Frequency Calculator

The Resonant Frequency Calculator computes the resonant frequency, angular frequency, Q factor, bandwidth, and half-power frequencies for LC and RLC circuits. It supports both series and parallel configurations, and can solve for frequency, inductance, or capacitance. All calculations include step-by-step MathJax formulas so you can follow the math.

What Is Resonant Frequency?

Resonant frequency is the natural oscillation frequency of an LC (inductor-capacitor) circuit. At this frequency, the energy stored in the inductor's magnetic field and the capacitor's electric field transfers back and forth with zero net reactance. The fundamental formula is:

$$f_0 = \frac{1}{2\pi\sqrt{LC}}$$

where $L$ is inductance in henries and $C$ is capacitance in farads. This frequency applies to both series and parallel LC/RLC circuits.

Series vs. Parallel Resonance

Series resonance: At the resonant frequency, the impedance drops to its minimum value ($Z = R$). The inductive and capacitive reactances cancel each other, allowing maximum current to flow. This makes series RLC circuits useful for band-pass filters and signal selection.

Parallel resonance: At the resonant frequency, the impedance reaches its maximum. The circulating current between the inductor and capacitor is very large, but the current drawn from the source is minimal. Parallel resonant circuits are used in oscillators, IF amplifiers, and tank circuits.

Quality Factor (Q) and Bandwidth

The quality factor describes how "sharp" the resonance peak is. A higher Q means a narrower bandwidth and more selective frequency response:

$$Q_{\text{series}} = \frac{\omega_0 L}{R} = \frac{1}{\omega_0 C R} \qquad Q_{\text{parallel}} = \frac{R}{\omega_0 L} = \omega_0 C R$$

Bandwidth is the frequency range between the half-power (-3dB) points:

$$BW = \frac{f_0}{Q}$$

How to Use This Calculator

Select solve mode — Choose whether to solve for resonant frequency ($f_0$), inductance ($L$), or capacitance ($C$).
Enter known values — Input the required component values with appropriate units. For RLC analysis, also enter a resistance value.
Choose circuit type — Select Series or Parallel. This affects the Q factor and impedance calculations (resonant frequency is the same for both).
Click Calculate — Press the button to compute all resonance parameters.
Review results — Examine the resonant frequency, Q factor, bandwidth, half-power frequencies, and the complete step-by-step derivation.

Practical Applications

Radio tuning — LC tank circuits select specific radio frequencies in AM/FM receivers
Filter design — Band-pass and band-stop filters rely on resonance to select or reject frequency ranges
Oscillator circuits — Colpitts, Hartley, and crystal oscillators use LC resonance to generate stable frequencies
Impedance matching — LC networks match impedances between stages in RF amplifiers and antenna systems
Power supply filtering — LC filters smooth rectified AC by rejecting ripple at specific frequencies

FAQ

What is resonant frequency?

Resonant frequency is the frequency at which an LC or RLC circuit naturally oscillates. At this frequency, the inductive reactance equals the capacitive reactance (X_L = X_C), causing energy to transfer back and forth between the inductor and capacitor. It is calculated as f₀ = 1/(2π√(LC)).

What is the Q factor of a circuit?

The quality factor (Q) measures how sharply a circuit resonates. A higher Q means a narrower bandwidth and more selective frequency response. For series RLC circuits, Q = ω₀L/R. For parallel RLC circuits, Q = R/(ω₀L). An ideal LC circuit without resistance has infinite Q.

What is the difference between series and parallel resonance?

In series resonance, impedance drops to its minimum (Z = R) at the resonant frequency, allowing maximum current flow. In parallel resonance, impedance reaches its maximum, resulting in minimum current from the source. The resonant frequency formula f₀ = 1/(2π√(LC)) is the same for both, but Q factor and impedance behavior differ.

What is bandwidth in a resonant circuit?

Bandwidth (BW) is the range of frequencies around the resonant frequency where the circuit response is at least 70.7% (1/√2) of its peak value. It is calculated as BW = f₀/Q. A higher Q factor results in a narrower bandwidth, meaning the circuit is more frequency-selective.

How do I find the required capacitance for a target frequency?

To find the required capacitance, rearrange the resonant frequency formula: C = 1/(4π²f₀²L). Enter your target frequency and known inductance in the calculator, select "Solve for Capacitance" mode, and it will compute the exact value needed.

Reference this content, page, or tool as:

"Resonant Frequency Calculator" at https://MiniWebtool.com/resonant-frequency-calculator/ from MiniWebtool, https://MiniWebtool.com/

by miniwebtool team. Updated: Mar 18, 2026

Developer API available: Run this tool from your app, automation, or agent with one JSON HTTP request. View API docs

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