There are three primary virus shapes, including a polyhedral shape, a helical shape and a complex virus shape. The polyhedral shape is like a dodecahedron with 12 sides, the helical shape is like a tube and the complex shape has long legs and a geometric head.
The shape of a virus is due to the viruses' nucleic acid and the arrangement and amount of proteins that it has. The diameter of the average virus ranges from 20 nanometers to 250 to 500 nanometers. The largest viruses that scientists know about range from 700 to 1,000 nanometers in length and they are approximately 500 nanometers in diameter.