A unit of length, 1 ångström (1 Å) equals 10-10 metres or 0.1 nanometres. It is named after the Swedish physicist Anders Jonas Ångström. This unit is sometimes used for measuring the diameters of atoms, which are typically around two to three Å. For a list of objects of size 1 to 10 Å, see 1e-10 m.
This is a non-SI unit, and is therefore considered deprecated. It is listed in Table 8 of the SI brochure ("Other non-SI units currently accepted for use with the International System"). BIPM explains "Table 8 lists some other non-SI units which are currently accepted for use with the SI to satisfy the needs of commercial, legal and specialized scientific interests. These units should be defined in relation to the SI in every document in which they are used. Their use is not encouraged.". Nanometres or picometres can easily be used instead.
However, despite its official deprecation, some scientists continue to use it anyway, because it is more convenient to use units which correspond to the items being discussed, e.g. atoms, grains of interstellar dust, etc.
See also: conversion of units.