An SI prefix is a prefix, that, when applied to a word, means to multiply that word by a particular power of ten. Examples of applications of SI prefixes include kilometer, megapixel, and gigabyte. These prefixes are often applied to units of measurement.

## Prefixes

The standard large and small SI prefixes are given below.

Name Value Factor/Divider Name Value
deca- 10 ten deci- 0.1
hecto- 100 hundred centi- 0.01
kilo- 1000 thousand milli- 0.001
mega- 106 million micro- 10-6
giga- 109 billion nano- 10-9
tera- 1012 trillion pico- 10-12
exa- 1018 quintillion atto- 10-18
zetta- 1021 sextillion zepto- 10-21
yotta- 1024 septillion yocto- 10-24

## Etymology

SI stands for "Système international", French for "international system".

## Extensions

### Andre Joyce's extension

Andre Joyce fabricated an extension to the system, noting that zetta and yotta seem related to sette (Italian "seven") and otto (Italian "eight.") Following the reverse-alphabet pattern, we have xova- \(= 10^{27}\), x + nove, and weica- \(= 10^{30}\), w + dieci. (The last letter has been changed to a to keep the pattern.) The pattern for the corresponding negative exponents, like deci-, centi-, and milli-, all end in -i.

From here, only the first syllable of the Italian number is used. We have:

• vunda- = \(10^{33}\), v + und(ici), vundi- = \(10^{-33}\)
• uda- = \(10^{36}\), u + (do)d(ici), udi- = \(10^{-36}\)
• treda- = \(10^{39}\), t + tred(ici), tredi- = \(10^{-39}\)
• satta- = \(10^{42}\), s + (qu)att(ordici), satti- = \(10^{-42}\)
• rinda- = \(10^{45}\), r + (qu)ind(ici), rindi- = \(10^{-45}\)
• qeda- = \(10^{48}\), q + (s)ed(ici), qedi- = \(10^{-48}\)
• pica- = \(10^{51}\), p + (d)ic(iasette), pici- = \(10^{-51}\)
• oca- = \(10^{54}\), o + (di)c(iotto), oci- = \(10^{-54}\)
• nica- = \(10^{57}\), n + (di)c(iannove), nici- = \(10^{-57}\)
• menta- = \(10^{60}\), m + (v)ent(i), menti- = \(10^{-60}\)

The system continues to zotta- = \(10^{255}\) and zotti- = \(10^{-255}\).

### Jim Blowers' extension

Initially Jim Blowers, like Andre Joyce, followed reverse-alphabet pattern and extends his system up to vigintillion:

• xona- = 1027
• weka- = 1030
• vunda- = 1033
• uda- = 1036
• treda- = 1039
• sorta- = 1042
• rinta- = 1045
• quexa- = 1048
• pepta- = 1051
• ocha- = 1054
• nena- = 1057
• minga- = 1060
• luma- = 1063

However, recently he changed this system and proposed his own system of prefixes up to 103,000. Here is a list of his prefixes:

### Hella-extension

Austin Sendek, a University of California student, started a (somewhat jocular) Facebook petition to make "hella-" the official SI prefix for 1027. "Hella" is a slang term originating out of Northern California, meaning "a lot of" or "very". The term has not become official, but both Google and Wolfram|Alpha have adopted it into their calculator systems.

### Other extensions

There are many other extensions to the SI prefixes, which are listed on the wiki's articles on extended SI prefixes - for example, see the article Prefix 1027.