# Unit of measure prefixes

Prefixes for units of measurement , unit prefixes , unit prefixes or prefixes or prefixes for short are used to form multiples or parts of units of measurement in order to avoid numbers with many digits.

## SI prefixes

SI prefixes are decimal prefixes defined for use in the International System of Units (SI) . They are based on powers of ten with integer exponents . A distinction is made between the name of the prefix and its symbol. The symbols are internationally uniform. The names differ depending on the language.

The prefixes in the SI
symbol Surname origin Value ( power , number , numeral )
Y Yotta ital. otto = eight 10 24 1,000,000,000,000,000,000,000,000 Quadrillion
Z Zetta ital. sette = seven 10 21 0.001,000,000,000,000,000,000,000 Trillion
E. Exa gr. hex = six 10 18 0.000.001,000,000,000,000,000,000 Trillion
P Peta gr. petannýnai = include everything / gr. pénte = five 10 15 0,000,000.001,000,000,000,000,000 Billiards
T Tera gr. téras = monster / gr. tetrákis = four times 10 12 0,000,000,000.001,000,000,000,000 trillion
G Giga gr. gigas = giant 10 9 0,000,000,000,000.001,000,000,000 billion
M. Mega gr. Mégas = large 10 6 0,000,000,000,000,000.001,000,000 million
k kilo gr. chílioi = thousand 10 3 0,000,000,000,000,000,000.001,000 thousand
H Hecto gr. hekatón = one hundred 10 2 0,000,000,000,000,000,000,000.100 Hundred
there Deka gr. Déka = ten 10 1 0,000,000,000,000,000,000,000.010 ten
- - - 10 0 0,000,000,000,000,000,000,000.001 one
d Deci Latin decimus = tenth 10 −1 0,000,000,000,000,000,000,000.000.1 tenth
c Centi lat. centum = hundred 10 −2 0,000,000,000,000,000,000,000.000.01 Hundredths
m Milli Latin mille = thousand 10 −3 0,000,000,000,000,000,000,000.000.001 Thousandths
μ Micro gr. Mikros = small 10 −6 0,000,000,000,000,000,000,000.000.000.001 Millionth
n Nano gr. nános = dwarf 10 −9 0,000,000,000,000,000,000,000.000,000,000,001 billionth
p Pico Spanish pico = tip / Italian piccolo = small 10 −12 0,000,000,000,000,000,000,000.000,000,000,000,001 Trillionth
f Femto skand. femton / femten = fifteen 10 -15 0,000,000,000,000,000,000,000.000,000,000,000,000,001 Billiardstel
a Atto skand.arton / atten = eighteen 10 −18 0,000,000,000,000,000,000,000.000,000,000,000,000,000,001 Trillionth
z Zepto lat. septem = seven 10 −21 0,000,000,000,000,000,000,000.000,000,000,000,000,000,000,001 Trillionths
y Yocto lat. octo = eight 10 −24 0,000,000,000,000,000,000,000.000,000,000,000,000,000,000,000,001 Quadrillionth

The characters for parts of a unit are written in lower case , while most characters for multiples of a unit are written in upper case . Exceptions to this system are, for historical reasons, the symbols for Deka (da), hecto (h) and kilo (k).

### typography

Like the unit symbols, the unit prefixes are written in upright, non-italic font, regardless of the font ( font ) of the surrounding text. No space is written between the unit prefix and the unit symbol.

The character " μ " is the only prefix symbol that comes from the Greek script, which has caused difficulties when typing and printing. In the electrotechnical literature, a “u” was therefore often used as a substitute. This was recommended in the International Standard ISO 2955 from 1983, which was withdrawn in 2001. For Germany, the recommendations of the DIN standard DIN 66030 “Information technology - Representation of unit names in systems with a limited number of characters” from May 2002 continue to apply. In Austria, the Measure and Verification Act provides for “μ”. When exchanging medical data according to the HL7 standard, the “u” is permitted instead of “μ”.

### Combination of SI prefixes and units

• The combination of the prefix and the unit symbol creates a new unit symbol that cannot be separated when the line breaks .
• A maximum of one prefix is ​​used per unit.
• SI prefix characters and the SI prefix names can not alone, but only together with unit symbols are used and unit names.
• No prefixes are applied to the derived SI unit 1 of quantities of the dimension number .
• The time units minute (min), hour (h), and day (d) are not used with prefixes.
• The kilogram (kg) already uses “kilo”, so no further intentions are applied. Instead, the gram (g) is assumed.
• When exponentiating , the exponent for the prefix applies with; z. E.g .: 5 km² = 5 * (1000 m) ² = 5,000,000 m²
• "M" denotes both the unit " meter " and the prefix "milli" ( 11000 ). In order to avoid misunderstandings, the character "m" for meters is put in the last position in the case of compound units. A preceding "m" is interpreted as a prefix. Example: Nm stands for Newton meter , mN for Millinewton.

### Linguistic

The name of a unit prefix forms a compound word with the associated unit name. Examples are nanometers or milligrams. If it is clear from the context which unit is meant, this compound word is often shortened to the prefix in colloquial language. So we speak of kilos when kilograms (kg) are meant. In the technical field, the micrometer (μm) is briefly referred to as My [ myː ]; in English the term micron is common for micrometer. In Austrian, the abbreviation Deka is used for the unit of mass decagram (dag), among craftsmen also centi for centimeter (cm).

In the square measure hectares exceptionally disappears on the word joint the "o" what the of "hekto" double vowel avoids.

## Historical prefixes

Until 1960 the prefixes “ Myria ” (Gr. Μύριοι mýrioi = ten thousand) were standardized in France with the sign ma for 10 +4 times and dimi with the sign dm for 10 −4 times. Instead of myria , at the beginning of the 19th century, on a proposal by Thomas Young, z. T. also written myrio .

Until around 1900, “Centimeter” was written with a C in German .

Earlier in Germany also the symbol D and UK dk for goods Deka common in Austria the sign was dk required by law until the mid-1950s.

In DIN 1301 Part 1 of December 1993, the SI prefix for 10 −24 “Yocto” was written; this spelling was corrected to "Yokto" in the October 2002 edition .

## Prefixes for values ​​of electrical components

Until 1950, the electrical capacity of capacitors, but also the self-induction of coils, were given in cm (centimeters) of the CGS system of units . Sometimes pF (pico was Farad ) also written as μμF. For better legibility, often on small components, uF (see also section Typography ), MF or (in English) MFD is found instead of μF . ; KV instead of kV for voltage and MEGOHM instead of MΩ for resistance are also common.

## Colloquial use

In the parlance of Internet users, the SI prefix k is sometimes used in unusual contexts, e.g. B. for time and number of items. Compare also the particularly special case of the designation Y2K for the year 2000 problem or W2K for Microsoft Windows 2000 . In the commercial / technical environment, the prefix k is also often used with currency units, such as k €. The combination T € also used there does not come from the SI, but means “thousand euros”.

## Unit prefixes for binary multiples

In data processing , SI prefixes are also used for amounts of data ( bits and bytes ), but often in the meaning of binary prefixes (multiples of 1024, e.g. 2 10 , 2 20 , 2 30 etc.). To date, the SI prefixes are used as decimal prefixes or binary prefixes for data volumes depending on the context, possibly depending on the storage medium being considered, which leads to considerable deviations, especially with higher values.

The International Electrotechnical Commission , which is responsible for standardization in electrical engineering, has therefore first defined special binary prefixes based on the SI prefixes according to the table below in the standard IEC 60027-2 (replaced by IEC 80000-13: 2008) and recommends their use for Amount of data. The decimal SI prefixes should mean the same for datasets as for SI units (decimal prefixes). The International Bureau of Weights and Measures (BIPM) responsible for the SI prefixes also recommends the use of this standard:

symbol Surname value Difference to

Power of ten

Yi Yobi (2 10 ) 8 = 2 80 1,208,925,819,614,629,174,706,176 1.209 · 10 24 0x1 0000 0000 0000 0000 0000 hex 20.89%
Room Zebi (2 10 ) 7 = 2 70 1,180,591,620,717,411,303,424 1.181 · 10 21 0x40 0000 0000 0000 0000 hex 18.06%
egg Exbi (2 10 ) 6 = 2 60 1,152,921,504,606,846,976 1.153 · 10 18 0x1000 0000 0000 0000 hex 15.29%
pi Pebi (2 10 ) 5 = 2 50 1,125,899,906,842,624 1.126 · 10 15 0x4 0000 0000 0000 hex 12.59%
Ti Tebi (2 10 ) 4 = 2 40 1,099,511,627,776 1.100 · 10 12 0x100 0000 0000 hex 9.95%
Gi Gibi (2 10 ) 3 = 2 30 1,073,741,824 1.074 · 10 90 0x4000 0000 hex 7.37%
Wed Mebi (2 10 ) 2 = 2 20 1,048,576 1.049 · 10 60 0x10 0000 hex 4.86%
Ki Kibi (2 10 ) 1 = 2 10 1,024 1.024 · 10 30 0x400 hex 2.40%

The binary prefix symbol is created by appending - i to the corresponding decimal prefix symbol (Ki is capitalized in contrast to k). The name of a binary prefix, on the other hand, is formed by appending -bi to the first two letters of the corresponding decimal prefix name.

Example of usage: A Kibibyte is written as 1 KiB = 2 10 B = 1024 B, where B stands for byte.