The nanometre was formerly known as the millimicrometre – or, more commonly, the millimicron for short – since it is 1 / 1000 of a micron (micrometre), and was often denoted by the symbol mµ


The nanometre is often used to express dimensions on an atomic scale: the diameter of a helium atom, for example, is about 0.06 nm, and that of a ribosome is about 20 nm. The nanometre is also commonly used to specify the wavelength of electromagnetic radiation near the visible part of the spectrum: visible light ranges from around 400 to 700 nm.