The angstrom or ångström ([ˈɔŋstrøm]) is a unit of length equal to 10−10 m (one ten-billionth of a meter) or 0.1 nm. Its symbol is the Swedish letter Å.
The ångström is often used in the natural sciences and technology to express the sizes of atoms, molecules, and microscopic biological structures, the lengths of chemical bonds, the arrangement of atoms in crystals, the wavelengths of electromagnetic radiation, and the dimensions of integrated circuit parts. Atoms of phosphorus, sulfur, and chlorine are 1 Å in covalent radius, while a hydrogen atom is 0.25 Å; see atomic radius.
The unit was named after the Swedish physicist Anders Jonas Ångström (1814–1874). The symbol is always written with a ring diacritic, as in the Swedish letter. Although the unit's name is often written in English without the diacritics, the official definitions contain diacritics.