Activated charcoal is mainly characterized by its degree of adsorptive power. Total surface area (TSA) is one of the main parameters that is often used to market activated carbon products. TSA is a measure of the surface area available for sorption. It is important to realize that a carbon product may have a relatively high TSA and yet be locked up in pores too small for sorption to occur. A measure of micro-porosity is the iodine adsorption number, which is defined as the amount of I2 adsorbed per gram of charcoal (mg/g). A micro-porous activated carbon will also have a relatively high TSA.