First of all the measurement is a diagonal measurement, from one corner to the opposite corner.
A 32" CRT tube tv is traditionally measured from the outside of the tube to the outside of the tube, and the housing of the tv may cover up part of this. A plasma or LCD tv should be a measure of what you actually see.
Each manufacturer is different. Some might take liberties in how they advertise their products, and frequently they will measure the picture and round up to the next integer number.
You also have to consider the aspect ratio of the screen. The older analog tv's had one aspect ratio, then later we got wide screen tv's. Since screens are measured on the diagonal, the screen of a 32" wide screen is not as tall as the screen of a 32" tv with normal aspect ratio. If you had say a 19" conventional tv and you bought a 22" wide screen, you would find that people on your new tv were actually smaller than they were on the old tv. I did the calculation once and discovered that there was roughly difference of 20%. For instance a 32" widescreen was equal in height to a 26" old fashioned tv. Years ago my wife and I had bought a 36" tube tv. To replace it with a widescreen and not feel that we had a smaller picture, we would have to replace it with a 46".