Femtometre

Femtometre
The helium atom and perspective magnitudes
General information
Unit system	SI
Unit of	length
Symbol	fm
Conversions
1 fm in ...	... is equal to ...
SI base units	1×10−15 m
Natural units	6.1877×1019 ℓP  1.8897×10−5 a0
imperial/US units	3.9370×10−14 in

The femtometre (American spelling femtometer), symbol fm,^[1][2][3] (derived from the Danish and Norwegian word femten 'fifteen', Ancient Greek: μέτρον, romanized: metrοn, lit. 'unit of measurement') is a unit of length in the International System of Units (SI) equal to 10⁻¹⁵ metres, which means a quadrillionth of one metre. This distance is sometimes called a fermi and was so named in honour of Italian naturalized to American physicist Enrico Fermi, as it is a typical length-scale of nuclear physics.