The standard measurement for weight and quality of fabrics is grams per square meter, usually abbreviated as GSM. This is the accepted standard in the United States as well as in foreign countries. Towels and bath robes typically vary from 300 to 800 GSM; other fabrics may have values as low as 100 GSM. The same units are used for toilet paper and other tissues (18 to 22 GSM is typical) as well as paper towels (35 to 50 GSM is typical).
Occasionally I receive requests to convert these units to U.S. pounds (usually from U.S. visitors who are not comfortable with metric units). The reason grams per square meter are used even in the U.S. is that they are a more accurate indicator of quality than pounds. Let’s compare, for example, two towels both weighing 1.5 pounds (680 grams) but with different dimensions, as follows:
Towel A weighs 1.5 pounds (680 grams) and measures 26 by 52 inches (.66 by 1.32 meters).
Calculate the surface area by multiplying the length and width in meters: .66 times 1.32 equals .8712 square meter.
Divide the weight in grams (680) by .8712 and find that you have a 780 GSM towel—quite plush.
Towel B also weighs 1.5 pounds (680 grams) but is larger, measuring 34 by 68 inches (.864 by 1.727 meters).
Multiply .864 by 1.727 to determine the area: 1.4921 square meters.
Divide 680 grams by 1.4921 and find that this towel is only 455 GSM—nice but not nearly as plush as Towel A.
As you can see from these examples, there is no direct conversion between GSM and pounds; the total weight of the towel is actually the product of the GSM and the towel’s dimensions.
NOTE: The surface area of a bath robe would be harder to figure because of the various pieces and angles, so the GSM would be equally difficult to figure this way.