One can visualize microbial growth by using nutrients that support the growth of microbes. On agar plates growth can be observed as one cell becomes many, visible as a colony. Colonies are composed of millions of cells that as an aggregate are visible by eye. The colony becomes larger as the population grows. In liquid media growth is seen as increasing cloudiness or turbidity.

It is possible to quantify the growth of a microbial population in the liquid media by spreading some of the liquid onto a plate. Each colony that grows on the plate began as one cell, and the number of colonies shows the number of cells in the liquid sample.

If the sample has too many cells, individual colonies will merge together and will not be distinguished on a plate. Therefore it might be necessary to dilute the sample in order to "plate" a known fraction of that sample. Diluting the sample allows us to take a manageable volume of the culture to represent a smaller fraction of the population.