Bandwidth

How to use this calculator

Bandwidth is the range of frequencies a filter passes (or a resonant circuit responds to). In "f₀ & Q" mode use BW = f₀ / Q — higher Q gives a narrower band. In "f₁ & f₂" mode enter the two −3 dB frequencies and the tool returns BW = f₂ − f₁, the geometric‑mean resonance f₀ = √(f₁·f₂), and the implied Q. The −3 dB (half‑power) frequencies are also shown in the first mode.

What it means in a real circuit

Bandwidth and Q are two sides of the same coin and define selectivity. A narrow bandwidth (high Q) is needed to reject adjacent channels in a radio; a wide bandwidth (low Q) is needed to pass a whole signal band without distortion. Bandwidth also sets the time response: a narrow‑band filter rings longer. Use this to check that your resonant design gives the selectivity you need.