Having given an explanation of paper weights used internationally (ISO 536) and in the US this page covers conversions between weights and stock types used in the US and the weights used internationally. Below are tables for each stock type covering the commonly found weights within each stock type and its grammage equivalent.

Bond Stock Paper - gsm Conversions

Basis Weight	Grammage
13lb	49gsm
16lb	61gsm
20lb	75gsm
24lb	90gsm
28lb	105gsm
32lb	120gsm
36lb	135gsm
40lb	151gsm

Standard office paper in the USA is 20lb Bond Letter Size, which is equivalent to 75gsm paper. This makes it very similar to the 80gsm A4 paper that is most common in the UK and the rest of Europe.

24lb and 28lb Bond stock is very similar to the 90gsm and 110gsm paper often used by lawyers and accountants in the UK for formal correspondance.

Cover Stock - gsm Equivalents

Basis Weight	Grammage
50lb	135gsm
60lb	163gsm
65lb	176gsm
80lb	216gsm
90lb	243gsm
100lb	271gsm
110lb	298gsm
130lb	352gsm
160lb	433gsm

Cover stock is also known as Card stock and covers light card at the 50lb and 60lb end of the scale through to extremely heavyweight card at the 160lb end.

Index Stock - gsm Conversions

Basis Weight	Grammage
90lb	163gsm
110lb	203gsm
140lb	252gsm
170lb	328gsm
220lb	398gsm

Newsprint Stock - gsm Conversions

Basis Weight	Grammage
22lb	36gsm
28lb	46gsm
30lb	49gsm
32lb	52gsm
34lb	55gsm
35lb	57gsm

Note how 22lb Newsprint stock is a considerably lighter grade of paper than 20lb Bond, this is due to the uncut sheet size for Newsprint being significantly larger than that of Bond.

Book Stock - gsm Conversions

Basis Weight	Grammage
30lb	44gsm
40lb	59gsm
45lb	67gsm
50lb	74gsm
60lb	89gsm
70lb	104gsm
80lb	118gsm
90lb	133gsm
100lb	148gsm
120lb	178gsm