# 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).

• do you have any reference for this? – mrbm Jul 3 at 10:36

To get the PSD from your FFT values, square each FFT value and divide by 2 times the frequency spacing on your x axis.

PSDvalue=(fftValue^2.0)/(2.0*df)

If you want to check the output is scaled correctly, the area under the PSD should be equal to the variance of the original signal.