Integration:
An nmr spectrum consist of another piece of useful information that is called integration. Integration calculates the intensity of each signal and is proportional to the number of protons accountable for that signal. So, a signal because of a methyl group will be three times more intense than one because of a methine (CH) group.
On the nmr spectrum the integration signal is the sloping line above the signals as shown in figure. There is no complete scale to this line, but the relative heights of the integration over every signal are proportional to the number of protons responsible for every signal. Note that it is the height raise over the whole signal that should be measured (that is you measure the height increase over all the peaks in the coupling pattern).
One other thing to watch out for is the chance of OH or NH2 groups being present in a spectrum. These will as well be integrated, but can be distinguished from CH, CH2 and CH3 groups as the protons in the former disappear from the spectrum if the sample is shaken with D2O.
Figure: integration