Area density

The areal density (also known as area density, surface density, superficial density, areic density, mass thickness, or density thickness) of a two-dimensional object is calculated as the mass per unit area. The SI derived unit is: kilogram per square metre (kg·m−2). In the paper and fabric industries, it is called grammage and is expressed in grams per square meter (gsm); for paper in particular, it may be expressed as pounds per ream of standard sizes ('basis ream'). The areal density (also known as area density, surface density, superficial density, areic density, mass thickness, or density thickness) of a two-dimensional object is calculated as the mass per unit area. The SI derived unit is: kilogram per square metre (kg·m−2). In the paper and fabric industries, it is called grammage and is expressed in grams per square meter (gsm); for paper in particular, it may be expressed as pounds per ream of standard sizes ('basis ream').