What does femto mean?


Femto is a prefix used in SI system for the multiple 10-15 and its symbol is f. In 1964, it was incorporated into to the International System of Units (SI). It comes from the Danish word femten, which implies fifteen.


  1. The diameter of a proton is 1.66 femtometres.
  2. The HIV-1 virus has a mass of approximately 1 x 10-15 g or 1 fg.

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