Sallen-Key Filter Designer
Component values for a 2nd-order Sallen-Key low-pass — Butterworth, Bessel or Chebyshev, from one chosen capacitor.
Snap R to the nearest E96 value and re-check fc — a few percent shift is normal. Cascade two sections (Q pairing 0.54/1.31 for 4th-order Butterworth) for 80 dB/decade. The op-amp needs GBW ≥ 100×fc·Q; and the unity-gain Sallen-Key passes high frequencies through C1 when the op-amp runs out of steam — add a small RC after it for stop-band hygiene.
Sallen-Key Filter Calculator computes component values for a 2nd-order Sallen-Key low-pass with your chosen response — free, instant and private in your browser. Data-acquisition and audio designers needing clean 40 dB/decade anti-alias or smoothing stages 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 Sallen-Key Filter Designer
Sallen-Key Filter Calculator computes component values for a 2nd-order Sallen-Key low-pass with your chosen response using the standard engineering relation: fc = 1/(2πR√(C1C2)); Q = √(C1/C2)/2 — Butterworth wants C1 = 2·C2. Worked live: a 1 kHz Butterworth from C2 = 10 nF: C1 = 20 nF and R1 = R2 ≈ 11.3 kΩ. 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 Sallen-Key Filter Designer
- 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 Sallen-Key Filter Designer?
- ✓Implements the real formula — fc = 1/(2πR√(C1C2)) — with the substitution shown, not a black box
- ✓Built for data-acquisition and audio designers needing clean 40 dB/decade anti-alias or smoothing stages
- ✓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 sallen-key filter?+
Component values for a 2nd-order Sallen-Key low-pass with your chosen response follows fc = 1/(2πR√(C1C2)); Q = √(C1/C2)/2 — Butterworth wants C1 = 2·C2. For example, a 1 kHz Butterworth from C2 = 10 nF: C1 = 20 nF and R1 = R2 ≈ 11.3 kΩ. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
Butterworth, Bessel or Chebyshev — how do I choose?+
Butterworth: flattest passband, the general-purpose default. Bessel: best step response/constant delay — choose it before ADCs sampling transients and for audio crossovers. Chebyshev: steepest initial rolloff for a given order, paid for with passband ripple and ringing.
Why does my Sallen-Key stop filtering at very high frequencies?+
Above the op-amp's bandwidth its output impedance rises, and C1 couples input straight through — the response comes back UP. Harmless when the op-amp has ≥100× fc·Q of GBW; for hostile environments add a small passive RC after the stage.
Is the Sallen-Key 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