General Concepts: Virus Size

Viruses are generally much smaller than the bacteria and its average size varies from 25-300 nm in diameter. They are visible under electron microscope and only the largest and complex viruses are seen under light microscope with high resolution . Among all, the smallest viruses belong to the families Circoviridae, Parvoviridae and Picornaviridae which measure about 20 - 30 nm in diameter while the largest one belongs to Poxviridae that measures around 250-300 nm in diameter. Recently, scientists isolated a new form of virus that infects amoeba and grouped it under a separate family Mimiviridae. The members of the family Mimiviridae range from 400-800 nm in diameter.

 

On an average a bacterial cell is about 1400 nm in diameter while an average epithelial cell is about 20,000 nm. Considering both viruses and bacteria to be nearly spherical a bacterial cell has a volume about 30,000 times greater than a virus while an epithelial cell is about 60 million times larger.