FM Bandwidth Calculator

This tool calculates the bandwidth of a Frequency Modulation (FM) signal. It also finds the modulation index.


According to Carson’s rule states approximately 98% of the power of a frequency-modulated signal lies within a bandwidth given by the formula:

BT = 2*(Δf + fm)


  • Δf is the peak deviation of the instantaneous frequency from the carrier center frequency
  • fm is the highest frequency in the modulating signal

the modulation index β is given by Δf/fm

Example Calculation

A 5 kHz peak deviation of a 10 kHz audio signal results in a modulation index of 0.50 and a FM bandwidth of 30 kHz.

FM Calculators

These two calculators provide insight into the performance of FM transmitters and receivers


[1] Carson’s Rule on Wikipedia

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