Zepto (unit symbol z) is a unit prefix in the metric system denoting a factor of 10−21, i.e. 0.000000000000000000001.

Adopted into the International System of Units (SI) in 1991, it is derived from the Latin septem, seven, since it is equal to 1000−7.

Examples of its use:

SI prefixes
Prefix Base 10 Decimal English word Adoption[nb 1] Etymology
Name Symbol Short scale Long scale Language Derived word
yotta Y  1024 1000000000000000000000000  septillion  quadrillion 1991 Greek eight[nb 2]
zetta Z  1021 1000000000000000000000  sextillion  trilliard 1991 Latin seven[nb 2]
exa E  1018 1000000000000000000  quintillion  trillion 1975 Greek six
peta P  1015 1000000000000000  quadrillion  billiard 1975 Greek five[nb 2]
tera T  1012 1000000000000  trillion  billion 1960 Greek four[nb 2], monster
giga G  109 1000000000  billion  milliard 1960 Greek giant
mega M  106 1000000  million 1873 Greek great
kilo k  103 1000  thousand 1795 Greek thousand
hecto h  102 100  hundred 1795 Greek hundred
deca da  101 10  ten 1795 Greek ten
 100 1  one
deci d  10−1 0.1  tenth 1795 Latin ten
centi c  10−2 0.01  hundredth 1795 Latin hundred
milli m  10−3 0.001  thousandth 1795 Latin thousand
micro μ  10−6 0.000001  millionth 1873 Greek small
nano n  10−9 0.000000001  billionth  milliardth 1960 Greek dwarf
pico p  10−12 0.000000000001  trillionth  billionth 1960 Spanish peak, beak, little bit
femto f  10−15 0.000000000000001  quadrillionth  billiardth 1964 Danish fifteen
atto a  10−18 0.000000000000000001  quintillionth  trillionth 1964 Danish eighteen
zepto z  10−21 0.000000000000000000001  sextillionth  trilliardth 1991 Latin seven[nb 2]
yocto y  10−24  0.000000000000000000000001  septillionth  quadrillionth 1991 Greek eight[nb 2]
  1. ^ Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873.
  2. ^ a b c d e f Part of the beginning of the prefix was modified from the word it was derived from, ex: "peta" (prefix) vs "penta" (derived word).

ReferencesEdit

  1. ^ John Dell BE PhD (2009-03-25). "Mechanical engineering gone small - how to measure Zeptograms and Yoctograms using MEMS technology" (PDF). University of Western Australia. Engineers Australia. Retrieved 2020-05-14.
  2. ^ [https://science.sciencemag.org/content/370/6514/339 Zeptosecond birth time delay in molecular photoionization.
  3. ^ [https://www.sciencenewsforstudents.org/article/photon-journey-molecule-shortest-event-zeptosecond-physics Physicists have clocked the shortest time span ever. It's how long it took a chunk of light to cross a hydrogen molecule]