The bandwith of the peak value in PSD

Hi, everybody. i have a gaussian distributed signal and the autocorrelation function of this signal. according to the wiener-khinchin theorem, the fourier transform of the autocorrelation function is equal to the PSD of this signal. how can i calculate the frequency bandwidth of the max. peak value in this power spectral density? i try to use the command findpeaks, but when happen the same max. peak values more than one in the power spectral density graph, i don't find exactly the bandwith value. Is there any a formula to calculate this bandwith value?