The smallest viruses are about 17 nanometers in diameter, and the largest viruses are up to 1,000 nanometers (1 micrometer) in length. By comparison, the bacterium Escherichia coli is 2,000 nanometers in length, a cell nucleus is 2,800 nanometers in diameter, and an average eukaryotic cell is 10,000 nanometers in length.