The nanometre (symbol: nm) is a
unit used to
length in the
metric system. It is equal to one
billionth of a
metre (1 m / 1,000,000,000). The name combines the
SI prefix nano- (from the
Ancient Greek νάνος, nanos, "dwarf") with the parent unit name metre (from Greek μέτρον, metrοn, "unit of measurement"). It can be written in
scientific notation as 1×10−9 m.
The nanometre is often used to express very tiny
dimensions, such as measuring
atoms. The nanometre is also commonly used to measure the
electromagnetic radiation near the part of the
spectrum that can be seen by humans.
Visible light ranges from around 400 to 800 nm.
The nanometre was formerly called the millimicrometre (or the millimicron). This is because it is 1/1000 of a
micrometre, and was written with the symbol mµ (or sometimes µµ).