Nanometre

The nanometre is a standard unit of length in the International System of Units (SI), defined as one billionth of a metre. It is widely used in the physical sciences to describe dimensions at the atomic, molecular and nanoscale. Because many natural and engineered structures fall within this range, the nanometre has become a fundamental measure in fields such as nanotechnology, semiconductor fabrication, molecular biology and materials science.

Definition and scale

A nanometre, symbol nm, represents 1 × 10⁻⁹ metres, equivalent to 0.000000001 m. It also corresponds to 1000 picometres. Expressed fractionally, one nanometre is one thousand millionth of a metre. This scale is especially relevant to molecular dimensions: atoms and small molecules measure fractions of a nanometre, while larger biological assemblies and engineered nanomaterials typically span several to a few hundred nanometres.

Historical terminology

Before the adoption of modern SI nomenclature, the nanometre was known as the millimicrometre or, more commonly, the millimicron, indicating its relationship to the micrometre. Early literature sometimes used the symbol mμ for this submicrometre measurement, although this usage became obsolete as SI standards replaced non-systematic terms. The renaming to nanometre aligned with a consistent prefix-based hierarchy within the metric system.

Etymological origins

The term nanometre combines the prefix nano-—from Ancient Greek nanos, meaning “dwarf”—with metre, itself derived from Greek metron, meaning “measure”. This construction follows SI rules for naming multiples and submultiples of base units, enabling clear communication across scientific disciplines.

Scientific and technological applications

Because so many physical processes occur at or near this scale, the nanometre is central to modern research and technology.

• Atomic and molecular dimensions fall naturally within the nanometre range. A helium atom has a diameter of roughly 0.06 nm, while a ribosome, a complex cellular machine, measures about 20 nm.
• Electromagnetic wavelengths in the visible spectrum are commonly expressed in nanometres: visible light spans approximately 400–700 nm, corresponding to violet and red light respectively. The ångström (0.1 nm) was once standard in spectroscopy and crystallography but has largely been replaced by the nanometre.
• Nanotechnology relies extensively on the nanometre scale. Phenomena such as quantum confinement, surface reactivity and molecular self-assembly are governed by nanoscale dimensions.
• Semiconductor manufacturing uses nanometre-based nomenclature to denote characteristic feature sizes on integrated circuits. Since the late 1980s, designations such as “32 nm node” or “22 nm node” have been used as markers of miniaturisation in the International Technology Roadmap for Semiconductors, even when actual physical gate lengths differ from nominal node names.

Use in standards and digital encoding

The nanometre conforms to SI rules for unit spelling and notation. The International Bureau of Weights and Measures endorses nanometre as the international form, while nanometer appears in American usage. In Unicode, several compatibility blocks include symbols historically associated with submicrometre notation, although the SI-approved unit remains “nm”.