Using Grams to measure the thickness of paper is not a very accurate method. The reason for this is that grams are a measurement of weight and not thickness. This can lead to all sorts of confusion, because if you are compering the same types of paper then grams will give you a good idea. However this dose not apply when compering two different types of paper.
For example a dense paper such as coated gloss art 130gsm is actually quite a bit thinner that a bulky uncoated 100gsm letterhead paper. Indeed it is more like the same thickness as a typical 80gsm photocopier paper!
A much more accurate measure of paper is to use Microns. This is because a micron is a proper measurement of distance and not weight.
