A: There are three most commonly used metrics for describing paper weight or thickness – gsm, mil, and pounds.

GSM: The first is Grams per Square Meter (gsm), which measures mass per unit of area. A typical gsm for a good quality photo or proofing paper is 250. A thin bond paper might be 120 gsm. The higher the gsm, the heavier the paper.

Mils: The second metric is mil, which is a measure of thickness. A mil is 1/1000th of an inch. While there is a correlation between gsm and mil (more gsm usually means more mil), it is not an exact correlation. A photo paper and a fine art paper might both be 250 gsm, but a fine art paper is often less dense and might have a mil rating of 15 vs 10 for the photo paper.

Note: mil should not be confused with millimeters (mm). A 10 mil paper is about 0.25 mm thick.

Pounds: Lastly, there’s basis weight, which is described in terms of pounds. This metric is most commonly applied to cut sheet paper used in a typical office environment, like copier paper. Basis weight describes the weight in pounds of a ream of 500 sheets. A typical weight for copier paper is 24 pounds.