Size classification refers to the unit process where particles are sorted based on their size. This unit operation goes hand-in-hand with comminution to ensure that only adequately crushed/ground particles move further in the mineral processing circuit; size classification might also be used in concentration unit operations.

There are various methods that are used to conduct size classification, one of the most common and basic is screening. When sieving/screening is used as a means of size classification, materials are passed by gravity, shaken or washed through a screen/mesh. By passing material through a series screens, a spectrum of particles size classes may be obtained.