Generally speaking, the larger the specific surface area (BET) of activated carbon is, the greater the adsorption force will be, but this is not always the case. BET is an application parameter that measures the total surface area of activated carbon by adsorption of nitrogen or butane. Logically, the larger the BET, the greater the adsorption force. However, in practical applications, this concept has limitations because the pores of activated carbon can be classified as macropores, mesopores, and micropores. Sometimes only a portion of the pores are suitable for the entry of certain types of adsorbates of specific sizes.

In liquid-phase applications, the adsorption value of organic substances typically increases with the increase in molecular weight (molecular size) until the molecules become too large to enter the pores. The ideal activated carbon has a large number of pores that are just slightly larger than the adsorbate molecules. If the pores are too small, the adsorbates cannot enter; if they are too large, the specific surface area per unit volume will decrease.

In gas-phase applications, small molecules are adsorbed into micropores. In this case, the concept of total surface area is applicable. As for the adsorption of metal complexes by activated carbon, which involves the formation of chemical bonds, a larger BET is not necessarily better.