How do we interpret frequency from fft command in matlab? When I apply fft to a sampled function(@ Fs) and I get peaks at some values in the fft array. How do I know what frequency in Hertz does it correspond to?

  • \$\begingroup\$ watch out for the fact that MATLAB arrays are 1-based, not 0-based, so the DC (zero frequency) term is in array[1], not array[0] \$\endgroup\$
    – Neil_UK
    Commented Jul 3, 2019 at 17:05

1 Answer 1


The output of the fft function will go from 0 Hz to fs/2, then -fs/2 to almost 0. If you ignore the 2nd half (for purely real signals), the following works well:

For n samples at a sampling rate of fs, you can create a frequency axis, f with the following formula:

f = (0:n-1)/n*fs

This gives you freqs from fs/2 to almost fs, but if you overlook that...

The other option is to use the fftshift command on the fft output and revise the formula

f = (0:n-1)/n*fs-fs/2


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