RC High-Pass Filter Calculator
From one resistor and one capacitor, get the cutoff frequency above which a high-pass filter lets signal through, plus the RC time constant.
Two inputs, two answers
Enter the resistance and the capacitance (in microfarads) and the calculator returns the −3 dB cutoff frequency and the time constant at once.
Passes high, blocks low
A high-pass filter lets frequencies above the cutoff through and attenuates everything below it — including DC, which it blocks entirely.
What is an RC high-pass filter calculator?
One resistor and one cap in, a cutoff frequency out
An RC high-pass filter calculator turns two component values — a resistor R and a capacitor C — into the cutoff frequency that defines where the filter starts passing signal. A first-order RC high-pass is the simplest filter that blocks low frequencies and DC while letting higher ones through: the capacitor sits in series and the resistor to ground. It is used to remove DC offset, couple audio stages, strip low-frequency hum, and pass the fast edges of a signal. Pick R and C and the cutoff falls out of one short formula.
Enter the resistance and the capacitance (in microfarads) to get the cutoff frequency and time constant instantly.
Two short formulas, both built from the resistance R and the capacitance C (converted from microfarads to farads).
f_c = 1 / (2π × R × C)The time constant is τ = R × C, and the cutoff (−3 dB) frequency is f_c = 1 / (2π × R × C) — exactly the same cutoff formula as a low-pass filter built from the same parts. What differs is the pass band: a high-pass passes frequencies above f_c and attenuates those below it, whereas a low-pass does the opposite. Because you enter the capacitance in microfarads, the calculator first multiplies by one-millionth to get farads.
Suppose you build a high-pass coupling stage with R = 1 kΩ and C = 1 µF.
Convert the capacitance
1 µF × 0.000001 = 0.000001 F — the capacitance in farads.
Time constant
1000 × 0.000001 = 0.001 s — the RC time constant.
Cutoff frequency
1 / (2π × 1000 × 0.000001) ≈ 159.15 Hz — signal above this passes, below it is rolled off.
The cutoff frequency (about 159.15 Hz for the example) is the −3 dB point: at exactly f_c the output amplitude is about 70.7 % of the input, and the filter passes frequencies above it while rolling off everything below at 20 dB per decade. So a high-pass with a 159 Hz cutoff lets a 1 kHz tone through nearly untouched but heavily attenuates a 20 Hz rumble and blocks DC outright. The time constant τ (0.001 s here) is the same information in the time domain — it sets how quickly the filter responds. To raise the cutoff (pass only higher frequencies), shrink R or C; to lower it (let more low frequencies through), make them larger. Choosing the cutoff is about deciding what to keep: set it below your signal band and above the unwanted hum or offset you want gone.
The formulas are the standard first-order results, but a couple of practical points are worth keeping in mind.
First-order roll-off, loading, and tolerances
This is an ideal first-order passive high-pass: the roll-off below the cutoff is a gentle 20 dB per decade, not a sharp brick wall, so frequencies somewhat below f_c are only partly attenuated. The formula assumes the next stage draws no current; a low-impedance load downstream shifts the real cutoff, so buffer the output or account for the load. Real resistor and capacitor tolerances (often ±5 % to ±20 %, and electrolytics worse) move the measured cutoff from the computed value. For steeper roll-off or a precise corner, cascade stages or use an active filter.