How do I use FFT determine the revolutions per minute of the data?

A=dlmread('data.txt');  
a = A(:,1); % Time Samples in seconds. 
b = smooth(A(:,2)); 
c = smooth(A(:,3)); 

Fs = 1/a; % Frequency 
figure(3);
plot(Fs,fft(y));

figure(4);
plot(Fs,fft(z));

[dpb]

There's an example for one-sided PSD computed by FFT at the documentation for FFT that shows the steps...you'll get the peaks in frequency so will then need to convert to rpm.