RC Low-Pass Filter Calculator
Enter any two of R, C, and cutoff frequency to solve the third — first-order RC.
What it does: Compute the cutoff frequency of a first-order RC low-pass filter, or solve for the required R/C.
When to use it: When filtering noise, limiting bandwidth, or doing debouncing / anti-aliasing.
MEANS Signals below — mostly pass, and signals above it are attenuated.
No history yet. Each calculation is automatically saved to this device.
How to use the low-pass filter calculator
Enter two, solve one.
- 01
Enter two values
Fill in any two of R, C, and cutoff frequency fc, leaving the third blank. Supports
10k,100n,1kHz. - 02
Click Calculate
The tool solves for the value you left blank.
- 03
Read fc
fc is the −3dB corner: signals below it pass, signals above it are attenuated.
Common questions, answered in 3 minutes
Are the low-pass and high-pass formulas the same?
The first-order RC cutoff-frequency formula is the same, fc=1/(2πRC); the only difference is which component you take the output from (output across the capacitor = low-pass, output across the resistor = high-pass).
What point is fc?
The frequency where the gain drops to −3dB (about 0.707×), treated in engineering as the passband edge.
What if I want a steeper roll-off?
First-order RC is −20dB/decade. For something steeper you need multiple stages (cascaded) or active filtering (Sallen-Key, etc.).
What capacitor value should I pick?
It is common to first fix an easily available capacitor (e.g. 10nF/100nF) and then solve for the resistor — this tool supports that workflow.
Standards and sources referenced by this tool
| Item | Value / Formula | Source |
|---|---|---|
| Cutoff frequency | fc = 1/(2π·R·C) | First-order RC filter |
First-order RC formula, no external API.