Band-Pass Filter Calculator

Enter cutoff frequencies or component values to compute center frequency, bandwidth, and Q. Includes Show Work and presets.

How to Use

  1. Pick an input mode: Frequencies (fL, fH) or Components (R/C pairs).
  2. Enter values and choose units (Hz/kHz/MHz, Ω/kΩ, nF/µF, etc.).
  3. Read outputs: center frequency f0, bandwidth BW, and Q.
  4. Open Show Work to see formulas and steps in base units.
Filter Lab View
Band-pass behavior summary (computed from your inputs).
fL
—
f0
—
fH
—
Q
—
Status: —
Inputs & Settings
Switch between frequency-based solving and component-based solving.
Frequency mode
Lower cutoff frequency (must be > 0)
Upper cutoff frequency (must be greater than fL)
Center frequency
—
Bandwidth (BW)
—
Q factor
—
Show Work (step-by-step)
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Work is shown in base units (Hz, Ω, F) for clarity and consistency.

Reference

A practical band-pass can be formed by cascading a high-pass (sets fL) and a low-pass (sets fH). This calculator focuses on the cutoff-frequency math and the derived band metrics.

  • RC cutoff: fc = 1 / (2πRC)
  • Bandwidth: BW = fH − fL
  • Center frequency: f0 = √(fL · fH) (geometric mean)
  • Q factor: Q = f0 / BW
Note: Actual filter response depends on topology (passive RC vs active, order, loading). This tool provides standard first-order cutoff math and derived band metrics.

FAQ

What’s a “good” Q for a band-pass?

Higher Q means a narrower band (more selective). Lower Q means a wider passband.

Why is f0 the geometric mean?

For symmetric behavior on a log frequency scale, the midpoint between fL and fH is √(fL·fH).

Why might real results differ?

Real circuits include source/load impedance, component tolerances, and higher-order effects. Use this as a fast design/verification helper.

Tool Info

Last updated:

Updates may include topology presets, additional unit support, and edge-case handling.