Angstrom, an extremely small unit of length that is used primarily in expressing the wavelengths of visible light. The wavelengths of visible light range from about 4,000 angstroms (violet light) to about 7,600 angstroms (red light). One angstrom is equal to one hundred-millionth (0.00000001) of a centimeter, which is about four billionths (0.000000004) of an inch. The nanometer, a unit equal to 10 angstroms, is often used instead of the angstrom.

The angstrom was named for the Swedish physicist Anders Jonas Angstrom its abbreviation is A.