Intensity of Signals

The amount of energy absorbed (intensity) by a particular type of proton is directly proportional to the number of protons of that type.  The intensity of the HNMR signal (integrated area under each peak)  are proportional to the relative number of each type.  For example methyl t-butyl ether has 9 equivalent protons on the t-butyl group and 3 equivalent protons on the methyl group.  Thus the ratio of the intensities of these signals will be 9:3 or simply 3:1.   Integration only provides relative numbers of protons not absolute numbers.

How is the intensity measured or displayed?

How the relative intensities is determined and displayed is dependent upon the particular NMR you are using.  There are two common ways in which the intensities data is displayed.

Integration Lines
Most of the HNMR on easyochem use integration lines.  With integration lines you measure the vertical line distance from plateau to plateau.  So with are t-butyl methyl ether example you would measure distance T and M and take there ratio.  In this case the T:M is equal to 3:1.  Thus there are a ratio of 3 t-butyl protons for every 1 methyl proton.

Area Printed Above Each Signal
On some instruments the intensities (integrals) are printed above each signal.  Usually the smallest integration area is given a value f 1 and all other signals are relative to this .  For our t-butyl methyl ether case it would look as follows.

MTBE