Convert GSM to US Standards…
The chart below can be used to convert GSM paper weights to US paper weights.
Note: gsm = grams per square meter or g/m2. Weights in bold are commonly available.
Not all paper types are available in all weights. For example, it would be very unlikely that you could find 28# cover paper, but 20# bond paper is extremely popular. Most office printers and copy machines use 20# bond paper. Cover paper is usually the kind of paper one might use for things like business cards. A popular business card paper is, in fact, 100# cover.
While metric measurements are generally not used in the United States, they are extremely helpful in trying to remember which paper is heavier or thicker than another or to make a choice as to which paper to use. 110# index paper, for example, is commonly sold in office supply stores in the United States. But, note than it is 199 gsm, versus 271 gsm for 100# cover paper. So, if you were ordering business cards, you would likely prefer the heavier 100# cover paper. By looking at the metric weight, you can see immediately that the 100# cover paper is about 36% heavier than the 110# index paper.