A measure of the total surface area of a solid per unit mass or volume. It is used in catalysis and gas adsorption where a chemical reaction is promoted on the surface of a catalyst, or the rate of adsorption of a component is dependent on contact with a surface. The specific area of highly porous solids can be determined using the BET isotherm. The specific surface area of a gram of activated carbon is typically 500 m2. The SI units are m2 kg−1 or m2 m−3 (or m−1).