# Conversion of FFT to PSD

I would like to convert FFT data which is set of 396 values for 396 frequencies (from 4Hz to 399Hz by 1Hz) in unit of g's (gravitational akcceleration) to PSD in unit of (g^2)/Hz, is it possible? Thank you for your help.

If X is your fft data then you need to take Y=abs(X).^2; to convert it. Your frequency axis is f=4:399;. You can plot the result then using plot(f,Y).