Zeptometre (American spelling: zeptometer, symbol: zm) is an SI measure of length that is equal to 10^-21 (zepto-) of a metre. A zeptometer is 1/10 the diameter of an electron, and 1/10 000 the diameter of a proton or neutron.

• 1 zm = 1 × 10⁻²¹ metre

yoctometre << zeptometre << attometre

See also

• 1 E-21 m
• SI
• SI prefix
• Orders of magnitude