GSM (Grams per Square Meter) refers to the paper weight independent of the paper size. A higher GSM means a heavier and more durable paper, but not necessarily higher quality or thicker. Two sheets of paper can have the same GSM but one can be much thicker while the other might be thinner and more tightly packed. If you want to sketch or write on both sides, you’ll want paper with a higher weight. Standard printer paper is around 80gsm while a business card is around 400gsm.