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
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.
These two calculators provide insight into the performance of FM transmitters and receivers
 Carson’s Rule on Wikipedia