Size control is the process of separating bulk material into two or more products on basis of
their size. In mineral processing practices, two methods dominating size control processes
are: screening and classification. As shown in the following figure, while screening uses a
geometrical pattern for size control, classification uses behavior of particle’s (finer than 1
mm) motion in air or liquids (water) for size control.

Sizing is extensively used for size separations from 300 mm down to around 40 μm (micron),
although the efficiency decreases rapidly with fineness. Dry screening is generally limited to
material above about 5 mm in size, while wet screening down to around 250 μm is common.
Although there are screen types that are capable of efficient size separations down to 40
μm, sizing below 250 μm is also undertaken by classification. Selection between screening
and classification is influenced by the fact that finer separations demand large areas of
screening surface and therefore can be expensive compared with classification for high
throughput applications.