Viruses are much smaller than bacteria. The smallest viruses are about 17 nanometers in diameter, and the largest viruses are up to 1,000 nanometers in length. By comparison, the bacterium E. 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. The following are the average sizes of some specific common viruses (note: 1 nanometer is equal to 0.001 micrometers; the head of a pin is about 1,000 micrometers in diameter):