RC Filter Calculator (low/high-pass)
Cutoff frequency from R and C plus the exact gain and phase at any frequency — first-order filters done right.
The corner is gentle: at fc you're only −3 dB and the rolloff is 20 dB/decade, so an RC after a PWM pin needs fc ~100× below the PWM frequency for clean DC. Loading matters — the next stage's input impedance parallels C (or R) and shifts fc; keep the following stage ≥10× the filter R, or buffer with an op-amp.
RC Filter Calculator computes first-order RC low/high-pass cutoff and the exact response at any frequency — free, instant and private in your browser. Anyone smoothing PWM, de-noising sensors or AC-coupling audio use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About RC Filter Calculator (low/high-pass)
RC Filter Calculator computes first-order RC low/high-pass cutoff and the exact response at any frequency using the standard engineering relation: fc = 1/(2πRC); |H| = 1/√(1+(f/fc)²) for LP — 20 dB/decade rolloff. Worked live: 10 kΩ with 100 nF cuts off at 159 Hz — at 1 kHz the low-pass is already −16 dB. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use RC Filter Calculator (low/high-pass)
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use RC Filter Calculator (low/high-pass)?
- ✓Implements the real formula — fc = 1/(2πRC) — with the substitution shown, not a black box
- ✓Built for anyone smoothing PWM, de-noising sensors or AC-coupling audio
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate rc filter?+
First-order RC low/high-pass cutoff and the exact response at any frequency follows fc = 1/(2πRC); |H| = 1/√(1+(f/fc)²) for LP — 20 dB/decade rolloff. For example, 10 kΩ with 100 nF cuts off at 159 Hz — at 1 kHz the low-pass is already −16 dB. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
How far below the PWM frequency should my RC cutoff sit?+
For clean DC, put fc at 1/100th of the PWM rate or lower: ripple attenuation at the PWM fundamental is then ~40 dB. A 1 kHz PWM smoothed by fc = 10 Hz leaves ~1 % ripple but responds to changes in ~30 ms — the ripple/settling trade is yours to place.
Why did adding the next stage shift my cutoff?+
Loading: the following input impedance appears in parallel with the filter and re-tunes it. Keep the next stage ≥ 10× the filter's R, or buffer with an op-amp; cascading two passive RCs the same way costs accuracy AND only reaches a soggy 12 dB/octave.
Is the RC Filter Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
Related Electronics tools
PCB Trace Width Calculator (IPC-2221)
Minimum trace width for your current and temperature rise — IPC-2221 formula with copper weight, layer choice and a step-by-step worked example.
● LiveMicrostrip Impedance Calculator
Z₀ of a surface microstrip from width, height and εr (IPC-2141A), plus effective dielectric constant and propagation delay.
● LiveStripline Impedance Calculator
Characteristic impedance of an embedded stripline trace from geometry and εr — the inner-layer companion to the microstrip tool.
● Live