A nanometer is one billionth of which unit of measurement?

A nanometer (nm) is a unit of measurement that is equivalent to one billionth of a meter.

The nanometre was formerly known as the millimicrometre – or, more commonly, the millimicron for short.

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.