The R/C filter rolls off the frequency response at 6 dB per octave above the cutoff frequency. The position of the resistor and capacitor are swapped to change from low pass to high pass but the same calculation applies to both filters.

A low-pass filter (LPF) passes low-frequency signals but attenuates (reduces the amplitude of) signals with frequencies higher than the cutoff frequency.

A high-pass filter (HPF) passes high-frequency signals but attenuates (reduces the amplitude of) signals with frequencies lower than the cutoff frequency.

Input any two values in the form boxes and hit the Calculate button to find the remaining value.