The size of the virus can be measured by using the following methods:
1. Electron microscopy
2. Ultracentrifugation
3. Hemagglutination assay
4. Filtration through collodion membranes of known pore diameter
5. Counting the number of Plaque-forming units (PFU) in plaque assay
6. Measuring the Infectious Dose (ID50) and Lethal Dose (LD50)