A nanometer (nm) is a unit of length in the International System of Units (SI), equal to one billionth of a meter (0.000000001 m) and to 1000 picometers. It is used to measure things that are very small, such as atoms and molecules, which are typically measured in nanometers. Here are some examples to help visualize the size of a nanometer:

• 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, if the diameter of a marble was one nanometer, then the diameter of the Earth would be about one meter

It is difficult to imagine just how small a nanometer is, but using familiar and common objects for comparison can help understand more complex scientific concepts.