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Giga- (/ˈɡɪɡə/ or /ˈɪɡə/) is a unit prefix in the metric system denoting a factor of a short-scale billion or long-scale milliard (109 or 1,000,000,000). It has the symbol G.

Giga- is derived from the Greek word γίγας (gígas), meaning "giant". The Oxford English Dictionary reports the earliest written use of giga in this sense to be in the Reports of the IUPAC 14th Conférence Internationale de Chimie in 1947: "The following prefixes to abbreviations for the names of units should be used: G giga 109×."[1] However, it was already used in 1932 by the German organization Verband deutscher Elektrotechniker.[2]

When referring to information units in computing, such as gigabyte, giga may sometimes mean 1073741824 (230); this causes ambiguity. Standards organizations discourage this and use giga- to refer to 109 in this context too.[3][4][non-primary source needed] Gigabit is only rarely used with the binary interpretation of the prefix. The binary prefix gibi has been adopted for 230, while reserving giga exclusively for the metric definition.


In English, the prefix giga can be pronounced /ˈɡɪɡə/ (a hard g as in giggle), or /ˈɪɡə/ (a soft g as in gigantic, which shares giga's Ancient Greek root).[5] A prominent example of this latter pronunciation is found in the pronunciation of gigawatts in the 1985 film Back to the Future.

According to the American writer Kevin Self, a German committee member of the International Electrotechnical Commission proposed giga as a prefix for 109 in the 1920s, drawing on a verse (evidently "Anto-logie") by the German humorous poet Christian Morgenstern that appeared in the third (1908) edition of his Galgenlieder (Gallows Songs).[6][7] This suggests that a hard German [ɡ] was originally intended as the pronunciation. Self was unable to ascertain when the /dʒ/ (soft g) pronunciation came into occasional use, but claimed that as of 1995 it had returned to /ɡ/ (hard g).[8][9]

In 1998, a poll by the phonetician John C. Wells found that 84% of Britons preferred the pronunciation of gigabyte starting with /ɡɪ/ (as in gig), 9% with /dʒɪ/ (as in jig), 6% with /ɡaɪ/ (guy), and 1% with /dʒaɪ/ (as in giant).[10]

Common usage

Prefix Base 10 Decimal Adoption
[nb 1]
Name Symbol
quetta Q 1030 1000000000000000000000000000000 2022[11]
ronna R 1027 1000000000000000000000000000
yotta Y 1024 1000000000000000000000000 1991
zetta Z 1021 1000000000000000000000
exa E 1018 1000000000000000000 1975[12]
peta P 1015 1000000000000000
tera T 1012 1000000000000 1960
giga G 109 1000000000
mega M 106 1000000 1873
kilo k 103 1000 1795
hecto h 102 100
deca da 101 10
100 1
deci d 10−1 0.1 1795
centi c 10−2 0.01
milli m 10−3 0.001
micro μ 10−6 0.000001 1873
nano n 10−9 0.000000001 1960
pico p 10−12 0.000000000001
femto f 10−15 0.000000000000001 1964
atto a 10−18 0.000000000000000001
zepto z 10−21 0.000000000000000000001 1991
yocto y 10−24 0.000000000000000000000001
ronto r 10−27 0.000000000000000000000000001 2022[11]
quecto q 10−30 0.000000000000000000000000000001
  1. ^ Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873.

Binary prefix

The notation 1 GB represents 1,000,000,000 bytes or, in deprecated usage, 1,073,741,824 (230) bytes. Per IEC 60027-2 A.2 and ISO/IEC 80000 standards, the correct notation of 230 is gibi (symbol Gi).[13] One gibibyte (1 GiB) is 1,073,741,824 bytes or 1.074 GB. Despite international standards, the use of 1 GB = 230 B is widespread. A laptop advertised as having 8 GB has 8,589,934,592 bytes of memory: 8.59×109 B, or 8 GiB. [citation needed]

See also


  1. ^ "giga-, comb. form". Oxford English Dictionary. October 2011.
  2. ^ "Wireless Engineer, 1932, issue 05, p. 252" (PDF). Archived (PDF) from the original on 2022-03-28. Retrieved 2022-03-28.
  3. ^ "§3.1 SI prefixes". The International System of Units (SI) (PDF) (in French and English) (8th ed.). Paris: STEDI Media. 2006. p. 127. ISBN 92-822-2213-6. Archived (PDF) from the original on 2006-08-13. Retrieved 2007-02-25. [Side note:] These SI prefixes refer strictly to powers of 10. They should not be used to indicate powers of 2 (for example, one kilobit represents 1000 bits and not 1024 bits). The IEC has adopted prefixes for binary powers in the international standard IEC 60027-2: 2005, third edition, Letter symbols to be used in electrical technology — Part 2: Telecommunications and electronics. The names and symbols for the prefixes corresponding to 210, 220, 230, 240, 250, and 260 are, respectively: kibi, Ki; mebi, Mi; gibi, Gi; tebi, Ti; pebi, Pi; and exbi, Ei. Thus, for example, one kibibyte would be written: 1 KiB = 210 B = 1024 B, where B denotes a byte. Although these prefixes are not part of the SI, they should be used in the field of information technology to avoid the incorrect usage of the SI prefixes.
  4. ^ NIST Guide for the Use of the International System of Units (Appendix D. ref 5)
  5. ^ "SI prefixes and their etymologies". US Metric Association. Retrieved 27 November 2019.
  6. ^ Morgenstern, Christian (1917). Galgenlieder nebst dem 'Gingganz' (in German). Illustrated by Karl Walser (22 ed.). Berlin, Germany: Bruno Cassirer. p. 52 – via Project Gutenberg. [First four lines:] Im Anfang lebte, wie bekannt, / als größter Säuger der Gig-ant. / Wobei gig eine Zahl ist, die / es nicht mehr gibt, - so groß war sie! [These lines are the only appearance of gig in the book. Gigant is German for "giant"; cf. "gigantic".]
  7. ^ Morgenstern, Christian (1963). Gallows Songs: Christian Morgenstern's "Galgenlieder", Bilingual Edition: A Selection. Translated by Knight, Max. University of California Press. pp. 24–25. ISBN 9780520008847. Retrieved 20 February 2016. [Translation:] Of yore, on earth was dominant / the biggest mammal: the Gig-ant. / ("Gig" is a numeral so vast, / it's been extinct for ages past.)
  8. ^ Self, Kevin (October 1994). "Technically speaking". Spectrum. IEEE: 18.
  9. ^ Self, Kevin (April 1995). "Technically speaking". Spectrum. IEEE: 16.
  10. ^ Wells, J. C. (1998). LPD pronunciation preference poll 1998.
  11. ^ a b "On the extension of the range of SI prefixes". 18 November 2022. Retrieved 5 February 2023.
  12. ^ "Metric (SI) Prefixes". NIST.
  13. ^ "Definitions of the SI units: The binary prefixes". Retrieved 2023-04-05.
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