||Look up yoctometre in Wiktionary, the free dictionary.
The yoctometre (International spelling as used by the International Bureau of Weights and Measures; SI symbol: ym) or yoctometer (American spelling) is an SI measure of length that is equal to 10−24 (yocto) of a metre. A yoctometre is equivalent to 1/100,000 the diameter of a proton or neutron.
In terms of relative length of units, a yoctometre ranks as follows: Planck length << yoctometre << zeptometre. A yoctometre is 1/1000 of a zeptometre (1 zeptometre (zm) = 1,000 yoctometres).