It is a common practice to use Gram per Square Meter (abbr. GSM) as the thickness unit of non woven fabric and woven PP fabric. In the carrier bags industry, the most popular thickness of non woven fabric bags is 80 GSM. As for woven PP fabric bags, it is 130 GSM with lamination.
When it comes to cotton bags, we use ounce (abbr. Oz) to indicate how thick the cotton is. 1 Ounce = 28.3495231 Grams, but 1 Oz cotton fabric is not equivalent to 28.3495231 GSM. To measure the thickness of cotton, people take 1 square yard of cotton and weigh it. The weight in ounce is the thickness in Oz. 1 square yard = 0.836127 square meter. So when we convert 1 Oz cotton to GSM, it is 28.3495231 ÷ 0.836127 = 33.9057620433 GSM. The popular cotton bags vary from 5 Oz to 12 Oz.
Here we offer you a handy tool: fabric Oz-GSM convertor.
Oz = GSM
GSM = Oz