Cutoff Frequency Calculator

What Is Cutoff Frequency?

Cutoff frequency (corner frequency) is the point where a filter's output drops to about 70.7% (−3 dB) of its passband value. Below or above this frequency, RC and LC circuits begin to attenuate signals significantly.

Cutoff Frequency Formulas

RC filter:

$$f_c = \frac{1}{2\pi RC}$$

LC filter:

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

Example (RC): 1 kΩ and 1 µF give $f_c = 1/(2\pi \times 1000 \times 10^{-6}) \approx 159$ Hz.

Applications

Cutoff frequency defines audio crossover points, low-pass anti-aliasing filters, high-pass DC blocking, and resonant LC tank circuits in radios and power converters.

Frequently Asked Questions

What does −3 dB mean?

At cutoff, output power is half the passband value, which is a 3 dB drop in voltage amplitude (−3 dB ≈ 0.707 of peak).

RC vs LC — which should I use?

Use RC mode for resistor-capacitor filters. Use LC mode for inductor-capacitor resonant or tuned circuits.

What units does this calculator use?

Resistance in ohms, capacitance in microfarads (µF), and inductance in millihenries (mH).

Is cutoff the same as resonant frequency?

For LC circuits, the natural resonant frequency matches the formula shown. RC filters do not resonate; they roll off smoothly.

How do I convert cutoff to angular frequency?

Multiply by $2\pi$: $\omega_c = 2\pi f_c$ in radians per second.

Report

What Is Cutoff Frequency?

Cutoff Frequency Formulas

Applications

Frequently Asked Questions

Related Tools

Recent Visits