A nanometer (nm) is a unit of measurement for length within the metric system. It is equal to one billionth (1×10-9) of a meter. The symbol for nanometer is nm. The nanometer is often used to express dimensions on an atomic scale, such as the diameter of a helium atom, which is about 0.06 nm. The nanometer is also commonly used to specify the wavelength of electromagnetic radiation near the visible part of the spectrum, where visible light ranges from around 400 to 700 nm. To understand how small a nanometer is, it can be compared to objects that we know how big or small they are. For example, a human hair is about 60,000 – 100,000 nm wide, and a DNA molecule is ~2.5 nm in width.