RC Low-Pass Cutoff
Component values
Enter the resistor and capacitor; the −3 dB cutoff frequency appears live.
Cutoff frequency
How to use this calculator
An RC low‑pass filter passes low frequencies and attenuates high ones. Its cutoff (−3 dB) frequency is fc = 1 / (2πRC), set entirely by the product of the series resistor and the shunt capacitor. Enter R and C in any convenient units and the cutoff appears instantly, along with the time constant τ = RC and the angular cutoff ωc = 1/RC.
What it means in a real circuit
Below fc the signal passes almost unchanged; above it the output rolls off at −20 dB/decade (−6 dB/octave). RC low‑passes are the building block of smoothing, anti‑aliasing, and first‑order conditioning — e.g. softening a PWM signal, filtering sensor noise, or setting the "darkness" of a tone control. Choosing the cutoff is usually the first design decision: pick fc, then choose a convenient R and compute C (or vice‑versa).