In the International System of Units, the prefix "nano" means one-billionth, or 10-9; therefore, one nanometer is one-billionth of a meter. It’s difficult to imagine just how small that is, so here are some examples:
• A sheet of paper is about 100,000 nanometers thick.
• A strand of human DNA is 2.5 nanometers in diameter.
• There are 25,400,000 nanometers in one inch.
• A human hair is approximately 80,000–100,000 nanometers wide.
• A single gold atom is about a third of a nanometer in diameter.
On a comparative scale, a sphere with a diameter of 1 nanometer is to a softball as a softball is to the Earth. The illustration on the right has three visual examples of the size and the scale of nanotechnology, showing just how small things at the nanoscale actually are.