Zepto-

Zepto- (symbol z) is a unit prefix in the metric system denoting a factor of 10−21 or 0.000 000  000  000  000  000  001.

Adopted in 1991, it comes from the Latin septem, meaning "seven", since it is equal to 1000−7.

Examples of its use:


 * The electric charge on one electron: 160.217657 zeptocoulombs (zC).


 * One zeptomole (zmol) of substance contains 602 particles.
 * The human insulin molecule is roughly 10 zeptograms.