RC High Pass Filter Cutoff Calculator
A first-order RC high pass filter passes frequencies above its cutoff and attenuates those below it, the mirror image of a low pass. It is built from a series capacitor and a resistor to ground, and is the everyday way to block DC, remove low-frequency rumble, or couple amplifier stages. This calculator returns the cutoff frequency, the RC time constant, and the angular cutoff frequency from a resistor and capacitor value. Enter R in ohms and C in farads to size your high pass stage and see all the related frequency-domain figures at once.
RC high pass formula
time constant tau = R * C
cutoff frequency fc = 1 / (2 * pi * R * C)
angular cutoff omega = 2 * pi * fc = 1 / (R * C)
rolloff below cutoff = 20 dB per decade
At the cutoff the output amplitude is 1 divided by the square root of 2 (about 70.7 percent) of the input. The capacitor sits in series and the resistor across the output. R is in ohms, C in farads.
Filter notes
- Above the cutoff the signal passes nearly unchanged; below it, it is attenuated.
- The single-pole rolloff is 20 dB per decade, or about 6 dB per octave.
- High pass filters block DC and low-frequency offset or rumble.
- 1 nanofarad equals 0.000000001 farad; convert before entering.
- The cutoff formula is identical to the low pass; only the topology differs.
RC high pass filter: frequently asked questions
What is the RC high pass filter cutoff formula?
The minus-3-dB cutoff of a first-order RC high pass filter is fc = 1 / (2 * pi * R * C), the same expression as the low pass version. R is in ohms, C in farads, and the cutoff is in hertz. At the cutoff the output is about 70.7 percent of the input amplitude.
How is a high pass filter different from a low pass?
A high pass filter passes frequencies above the cutoff and attenuates those below it, the reverse of a low pass. Although the cutoff formula is identical, the components are arranged differently: the capacitor is in series and the resistor across the output.
What is the rolloff below the cutoff?
A single-pole RC high pass filter attenuates at 20 dB per decade below the cutoff (about 6 dB per octave). Each tenfold drop in frequency reduces the output amplitude tenfold. Above the cutoff, signals pass with little attenuation.
What is a common use for a high pass filter?
High pass filters block DC and remove low-frequency rumble or offset while letting higher frequencies through. They are used as coupling capacitors between amplifier stages, in audio to cut rumble, and to remove slow drift from sensor signals.
Does the time constant mean the same thing here?
Yes. The time constant tau = R * C is the same product, and the cutoff is still fc = 1 / (2 * pi * tau). The difference between high and low pass is in the circuit topology, not in the cutoff or time-constant relationship.
Official sources
- NIST: SI units (hertz, ohm, farad).
- NASA Glenn Research Center: RC filter and reactance fundamentals.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.