A unit of length equal to 10⁻¹⁵ metres. It is primarily used in particle physics to measure the size of atomic nuclei and subatomic particles. It shares the exact same value as the older fermi unit.
Heard on the job
The charge radius of a proton is roughly 0.84 femtometres.
Insider tip
Physicists often use the historic name 'fermi' interchangeably with femtometre, as both share the same 'fm' symbol.
Also heard as
- fermi