A nanometre (American spelling: nanometer, symbol: nm) is 1.0×10−9 metres — or one billionth of a metre. It is an SI measure of length, commonly used in measuring the wavelengths of visible light (400 nm to 700 nm), ultraviolet radiation and gamma rays; amongst other things.
In older (e.g. 1958) texts, the nm is sometimes denoted "mµ" for "millimicron", based on the old term "micron" for a micrometre. Double prefixes are not allowed in SI, and this is never seen in modern writing or speech.
picometre << nanometre << micrometre
See also
