In general, the larger the specific surface area (BET) of activated carbon, the greater its adsorption capacity. However, this is not always the case. BET is an application parameter used to measure the total surface area of activated carbon using nitrogen or butane adsorption methods. In theory, the greater the BET, the greater the adsorption capacity. However, this concept has limitations in practical applications, as activated carbon has pores of different sizes, including large pores, medium pores, and micropores. Sometimes only a portion of the pores are suitable for the entry of certain sized adsorbates.

In liquid phase applications, the adsorption value of organic compounds generally increases with increasing molecular weight (molecular size). Until the molecule is too large to enter the pores. The ideal activated carbon would have a large number of pores slightly larger than the adsorbate molecule. Pores that are too small prevent the adsorbate from entering, while pores that are too large reduce the surface area per unit volume.

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, it involves the formation of chemical bonds, and it is not necessarily the case that BET is greater the better.