Zetta is a decimal unit prefix in the metric system denoting a factor of 1021 or 1000000000000000000000. The prefix was added as an SI prefix to the International System of Units (SI) in 1991 and has the symbol Z.
Zetta is evocative of the Latin numeral septem, meaning "seven". Therefore it was used to denote the seventh power of 1000.
A prefix of the same value, hepta, was informally introduced a few years before the promulgation of zetta. It was formed from the Greek ἑπτά (hepta), also meaning "seven". Hepta never received official sanction and is obsolete. Zeta (ζήτα), although the 6th letter of the modern and classical Greek alphabet, denotes a value of seven (7) when used as a numeral.
- The mass of Earth's atmosphere is approximately 5 zettagrams (Zg).
- The volume of seawater in the Earth's oceans is approximately 1.369 zettalitres (ZL).
- The Avogadro constant is 602.2 Zmol−1.
- Estimates of the diameter of the Milky Way Galaxy are between 0.9 and 1.7 zettametres (Zm).
- As of 2009[update], the entire World Wide Web was estimated to contain close to half a zettabyte. The zebibyte (ZiB) is a related unit that uses a binary prefix, and means 10247 bytes.
- Prefixes adopted before 1960 already existed before SI. 1873 was the introduction of the CGS system.
- "Resolution 4 of the 19th CGPM (Conférence Générale des Poids et Mesures)". BIPM (Bureau International des Poids et Mesures). Retrieved 2009-05-16.
Les noms zepto et zetta évoquent le chiffre sept (septième puissance de 103) et la lettre « z » remplace la lettre « s » pour éviter le double emploi de la lettre « s » comme symbole. The names zepto and zetta are evocative of the numeral sept (seventh power of 103) and the letter 'z' is substituted for the letter 's' to avoid the duplicate use of the letter 's' as a symbol.
- Williams, David R. (December 16, 2016), Earth Fact Sheet, NASA Goddard Space Flight Center, retrieved 2018-01-21.
- Richard Wray (2009-05-18). "Internet data heads for 500bn gigabytes". The Guardian.