Low Pass Filter Calculator

RC Low-Pass Filter Cutoff Frequency

A first-order RC low-pass filter attenuates frequencies above its cutoff. It is widely used for audio tone control, anti-aliasing, and removing high-frequency noise from analog signals.

Formula

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

Rearranging gives $R = 1/(2\pi f_c C)$ and $C = 1/(2\pi f_c R)$. At $f_c$, the output amplitude is about 3 dB below the passband level.

Design Example

A $3.3\,\text{k}\Omega$ resistor with a $47\,\text{nF}$ capacitor gives $f_c \approx 1.03\,\text{kHz}$. Standard component values are convenient, but always account for tolerance when building hardware.

Frequently Asked Questions

What does a low-pass filter do?

It passes low-frequency components and attenuates high frequencies. Above the cutoff frequency, response typically falls at about 20 dB per decade for a first-order RC filter.

What is the −3 dB point?

The cutoff frequency $f_c$ is where output power drops to half its passband value, which is a −3 dB attenuation in amplitude.

Can I solve for any one of R, C, or f_c?

Yes. Enter the other two values and select which quantity you want to calculate. The calculator uses the same RC relationship in all three modes.

Does this include op-amp active filters?

This tool covers the passive RC low-pass filter. Active op-amp filters use related cutoff formulas but also introduce gain and different topologies.

What units should I use for capacitance?

Select pF, nF, µF, mF, or F. The calculator converts internally to farads before applying $f_c = 1/(2\pi RC)$.

Report

RC Low-Pass Filter Cutoff Frequency

Formula

Design Example

Frequently Asked Questions

Related Tools

Recent Visits