
This might help some. The 'GSM' column is a metric measurement which is the actual weight of one sheet of media cut 1 x 1 meter square. GSM is nice because it is a uniform scale to estimate a paper's weight and thickness.
Note; US paper weights are enough to drive a person nuts. Here is a copy and paste from a web site which attempts to describe the nuttiness...
Quote:
The U.S. Basis (not basic) Weights, are the most confusing, simply because the same paper can yield different values based on the "Basis Weight" applied while manufacturing the paper. And higher values don't always equate to heavier/thicker print media. For example, a sheet of 100lb Text paper is actually much thinner than an 80lb Cover stock.
The "Basis Weight" is defined as the weight of 500 sheets of paper in its basic unit uncut size, which means before being cut to Letter size or Legal size, the paper is weighed and categorized. The most common sizes, some of which you may recognize, are Bond, Text, Book, Cover, Index and Tag. An uncut sheet of Bond paper is 17 x 22 inches, while an uncut sheet of Cover paper is 20 x 26 inches. If 500 sheets of Bond paper (17 x 22 inches) weigh 20 lbs, then a ream of paper cut to Letter size will be labeled as 20 lb. And if 500 sheets of Cover paper (20 x 26 inches) weigh 65 lbs, then a ream of this paper trimmed to tabloid size would be marked as 65lb. This may be a lot to grasp, but don't feel overwhelmed! Often professional printers don't keep track of all the permutations. Based on experience from using a small subset, they have a pretty good idea of what to expect when reaching for a 24lb Bond versus a 60lb Cover versus a 110lb Index.