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Bandwidth Of A Filter Calculator

Work out bandwidth of a filter instantly with clear inputs, formula shown and shareable results.

About Bandwidth Of A Filter Calculator

Bandwidth of a resonant filter is centre frequency divided by Q, and the two -3 dB points sit geometrically either side of f0. Rolloff outside the passband is about 6 dB per octave per order, so a higher-order filter rejects out-of-band signals far more steeply.

Formula

Filter bandwidth

BW = f0 / Q; the cutoffs are geometrically centred on f0; rolloff = 6 dB/octave per order

Worked example

With the default values below, Bandwidth Of A Filter Calculator returns 3 dB bandwidth of 214.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Centre frequency
10.7 MHz
Quality factor
50
Filter order
2

Results

3 dB bandwidth
214.00 kHz
Lower cutoff frequency
10.5935 MHz
Upper cutoff frequency
10.8075 MHz
Skirt rolloff
12 dB/octave

Step by step

  1. 1Values used
  2. 2Filter bandwidth
  3. 33 dB bandwidth= 214.00 kHz
  4. 4Lower cutoff frequency= 10.5935 MHz
  5. 5Upper cutoff frequency= 10.8075 MHz
  6. 6Skirt rolloff= 12 dB/octave

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or fees or charges into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

Frequently Asked Questions

Are the cutoffs symmetric about f0?

Geometrically, not arithmetically: f0 is the geometric mean of the two cutoffs, so on a log frequency axis they look symmetric.

What does high Q cost?

Narrow bandwidth means longer settling time and greater sensitivity to component drift, so Q above a few hundred needs crystals or resonators.

Related Calculators

Bandwidth Of A Filter Calculator – Calculate 3 dB bandwidth