Size of Bacterial Cells

Bacteria are very small microscopic structures. They vary in size from 0.2-2.0 micrometers (µm) in diameter and 0.5-5.0 µm in length. The smallest known bacteria are the members of the genus Mycoplasma. They are about 0.3 µm in diameter. Recently, nanobacteria or ultramicrobacteria (0.2-0.05 µm in diameter) have been reported.

Escherichia coli, the most commonly studied bacteria is about 1.1-1.5 µm wide and 2.0-6.0 µm long. Some bacteria are very large in size and are visible to unaided eye like Epulopiscium fishelsoni and Thiomargarita namibiensis. E. fishelsoni is rod shaped and about 600 µm in length and 80 µm in diameter. 

As bacteria are very small in size, they have large surface area to volume ratio. Thus all the internal parts of the cell are very close to the surface. This makes nutrients to be easily and quickly available to all the parts of the cell and thereby helping in the rapid uptake and intracellular distribution of nutrients and excretion of wastes.