In Microbiology, a unit forming colonies (CFU), the unit is to estimate the number of bacterial cells or fungal infection, live in a sample is used. The order of "live", the ability to reproduce through binary division, under controlled conditions.

In order to count the units forming colonies, etc. is needed, first, the microbes in the culture medium, grow. In this method, unlike the methods of microscopic, in which also the dead cells and the live count. in here, only live cells counted. For this that Colony, the surface of the culture medium, etc. are visible should be largely grown.

The purpose of counting the colonies, plate, estimate the number of cells based on their ability to grow and create colonies under the conditions of nutrition, temperature and specific time. In terms of theory, a living cell must be able to grow through reproduction, colony formation.