A micron, also called a micrometer, is a unit of length equivalent to a millionth of a meter, or one thousandth of a millimeter, or one thousand nanometers. The smallest objects readily visible to the unaided human eye measure about 40 to 50 microns. A typical bacterium has a length of one to ten microns, a strand of spider web silk is three to eight microns in diameter, and human hairs range from ten to 200 microns in diameter. Cells of living organisms can range between one and hundreds of microns in diameter. The longest human chromosome, which contains about two thousand genes, is approximately ten microns in length. Transistors and other microscopic components in the most advanced electronic integrated circuit chips have widths only a tiny fraction of a micron and are thus instead measured in nanometers.