Nanometre

The nanometre (symbol nm) is a unit of length in the metric system equal to 10^-9 metres. It is not a base SI unit, but it is accepted for use with SI. The prefix nano- denotes one billionth, so one nanometre is one thousandth of a micrometre and one millionth of a millimetre. In American English the spelling is nanometer, while nanometre is the British variant; the symbol nm remains the same.

Nanometres are used to express dimensions at atomic and molecular scales. They are suitable for describing typical sizes in nanoscience and nanotechnology, such as the diameters of atoms (roughly 0.1–0.5 nm), molecular dimensions, and DNA base-pair spacing (about 0.34 nm). The scale is also relevant for nanomaterials, nanoparticles, and feature sizes in advanced electronics, where components and structures are often measured in a few to a few tens of nanometres. Wavelengths of visible light (roughly 400–700 nm) are much larger than a nanometre, underscoring why interactions at the nanoscale require specialized techniques.

Commonly used related units include the ångström (Å), where 1 Å = 0.1 nm, and the micrometre (µm), where 1 µm = 1,000 nm. Measurement and characterization at the nanometre scale rely on tools such as electron microscopes and scanning probe techniques, enabling imaging and manipulation of structures at sub-nanometre resolutions. The nanometre remains a practical unit for conveying the sizes encountered in condensed matter physics, chemistry, biology, and materials science.