Answer: Nanometer
Step-by-step explanation:
The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American spelling) is a unit of length in the metric system, equal to one billionth (short scale) of a metre (0.000000001 m).
...
Nanometer
imperial/US units 3.2808×10−9 ft 3.9370×10−8 in