Size of Pores (IUPAC Standard)

Porous material are classified according to the size of pores: material with pores less than 2 nm are called micropores , materials with pores between 2 and 50 nm are called mesopores , and material with pores greater than 50 nm are macrospores

Sing, K. S. W. et al. Reporting Physisorption Data for Gas/Solid Systems. Pure & Appl. Chem. 57, 603-619 (1985).