Kilo is a
decimal
The decimal numeral system (also called the base-ten positional numeral system and denary or decanary) is the standard system for denoting integer and non-integer numbers. It is the extension to non-integer numbers (''decimal fractions'') of th ...
unit prefix
A unit prefix is a specifier or mnemonic that is added to the beginning of a unit of measurement to indicate multiples or fractions of the units. Units of various order of magnitude, sizes are commonly formed by the use of such prefixes. The Metric ...
in the
metric system
The metric system is a system of measurement that standardization, standardizes a set of base units and a nomenclature for describing relatively large and small quantities via decimal-based multiplicative unit prefixes. Though the rules gover ...
denoting multiplication by one
thousand (10
3). It is used in the
International System of Units
The International System of Units, internationally known by the abbreviation SI (from French ), is the modern form of the metric system and the world's most widely used system of measurement. It is the only system of measurement with official s ...
, where it has the symbol k, in
lowercase
Letter case is the distinction between the letters that are in larger uppercase or capitals (more formally ''majuscule'') and smaller lowercase (more formally '' minuscule'') in the written representation of certain languages. The writing system ...
.
The prefix ''kilo'' is derived from the
Greek word (), meaning "thousand".
In 19th century English it was sometimes spelled chilio, in line with a
puristic opinion by
Thomas Young.
As an opponent of suggestions to introduce the metric system in Britain, he qualified the nomenclature adopted in France as barbarous.
Examples
* one
kilogram
The kilogram (also spelled kilogramme) is the base unit of mass in the International System of Units (SI), equal to one thousand grams. It has the unit symbol kg. The word "kilogram" is formed from the combination of the metric prefix kilo- (m ...
(kg) is 1000
gram
The gram (originally gramme; SI unit symbol g) is a Physical unit, unit of mass in the International System of Units (SI) equal to one thousandth of a kilogram.
Originally defined in 1795 as "the absolute Mass versus weight, weight of a volume ...
s
* one
kilometre
The kilometre (SI symbol: km; or ), spelt kilometer in American English, American and Philippine English, is a unit of length in the International System of Units (SI), equal to one thousand metres (kilo- being the SI prefix for ). It is the ...
(km) is 1000
metre
The metre (or meter in US spelling; symbol: m) is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of of ...
s
* one
kilojoule
The joule ( , or ; symbol: J) is the unit of energy in the International System of Units (SI). In terms of SI base units, one joule corresponds to one kilogram- metre squared per second squared One joule is equal to the amount of work don ...
(kJ) is 1000
joule
The joule ( , or ; symbol: J) is the unit of energy in the International System of Units (SI). In terms of SI base units, one joule corresponds to one kilogram- metre squared per second squared One joule is equal to the amount of work d ...
s
* one kilolitre (kL) is 1000
litre
The litre ( Commonwealth spelling) or liter ( American spelling) (SI symbols L and l, other symbol used: ℓ) is a metric unit of volume. It is equal to 1 cubic decimetre (dm3), 1000 cubic centimetres (cm3) or 0.001 cubic metres (m3). A ...
s
* one kilobaud (kBd) is 1000
bauds
* one kilohertz (kHz) is 1000
hertz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or Cycle per second, cycle) per second. The hertz is an SI derived unit whose formal expression in ter ...
* one kilodalton (kDa) is 1000
daltons
* one
kilobit (kb) is 1000
bits
* one
kilobyte
The kilobyte is a multiple of the unit byte for Computer data storage, digital information.
The International System of Units (SI) defines the prefix ''kilo-, kilo'' as a multiplication factor of 1000 (103); therefore, one kilobyte is 1000&nbs ...
(kB) is 1000
byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable un ...
s
* one kiloohm is (kΩ) is 1000
ohm
Ohm (symbol Ω) is a unit of electrical resistance named after Georg Ohm.
Ohm or OHM may also refer to:
People
* Georg Ohm (1789–1854), German physicist and namesake of the term ''ohm''
* Germán Ohm (born 1936), Mexican boxer
* Jörg Ohm (1 ...
s
* one
kilosecond (ks) is 1000
seconds
The second (symbol: s) is a unit of time derived from the division of the day first into 24 hours, then to 60 minutes, and finally to 60 seconds each (24 × 60 × 60 = 86400). The current and formal definition in the International System of ...
*one
kilotonne (kt) is 1000
tonnes
The tonne ( or ; symbol: t) is a unit of mass equal to 1,000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton in the United States to distinguish it from the non-metric units of the s ...
By extension, currencies are also sometimes preceded by the prefix kilo-:
* one kiloeuro (k€) is 1000
euro
The euro (currency symbol, symbol: euro sign, €; ISO 4217, currency code: EUR) is the official currency of 20 of the Member state of the European Union, member states of the European Union. This group of states is officially known as the ...
s
* one kilodollar (k$) is 1000
dollar
Dollar is the name of more than 25 currencies. The United States dollar, named after the international currency known as the Spanish dollar, was established in 1792 and is the first so named that still survives. Others include the Australian d ...
s
kilobyte
For the kilobyte, a second definition has been in common use in some fields of
computer science
Computer science is the study of computation, information, and automation. Computer science spans Theoretical computer science, theoretical disciplines (such as algorithms, theory of computation, and information theory) to Applied science, ...
and information technology. It uses ''kilobyte'' to mean 2
10 bytes (= 1024 bytes), because of the
mathematical coincidence that 2
10 is approximately 10
3. The reason for this application is that digital hardware and architectures natively use
base 2 exponentiation, and not
decimal
The decimal numeral system (also called the base-ten positional numeral system and denary or decanary) is the standard system for denoting integer and non-integer numbers. It is the extension to non-integer numbers (''decimal fractions'') of th ...
systems.
JEDEC memory standards still permit this definition, but acknowledge the correct SI usage.
NIST comments on the confusion caused by these contrasting definitions: "Faced with this reality, the ''IEEE Standards Board'' decided that IEEE standards will use the conventional, internationally adopted, definitions of the SI prefixes", instead of kilo for 1024.
Definition of binary prefixes at NIST
/ref> To address this conflict, a new set of binary prefix
A binary prefix is a unit prefix that indicates a multiple of a unit of measurement by an integer power of two. The most commonly used binary prefixes are kibi (symbol Ki, meaning ), mebi (), and gibi (). They are most often used in inform ...
es has been introduced, which is based on powers of 2. Therefore, 1024 bytes are defined as one kibibyte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable un ...
(1 KiB).
Exponentiation
When units occur in exponentiation
In mathematics, exponentiation, denoted , is an operation (mathematics), operation involving two numbers: the ''base'', , and the ''exponent'' or ''power'', . When is a positive integer, exponentiation corresponds to repeated multiplication ...
, such as in square and cubic forms, any multiplier prefix is considered part of the unit, and thus included in the exponentiation.
* 1 km2 means one square kilometre or the area of a square
In geometry, a square is a regular polygon, regular quadrilateral. It has four straight sides of equal length and four equal angles. Squares are special cases of rectangles, which have four equal angles, and of rhombuses, which have four equal si ...
that measures 1000 m on each side or 106 m2 (as opposed to 1000 square meters, which is the area of a square that measures 31.6 m on each side).
* 1 km3 means one cubic kilometre or the volume of a cube
A cube or regular hexahedron is a three-dimensional space, three-dimensional solid object in geometry, which is bounded by six congruent square (geometry), square faces, a type of polyhedron. It has twelve congruent edges and eight vertices. It i ...
that measures 1000 m on each side or 109 m3 (as opposed to 1000 cubic meters, which is the volume of a cube that measures 10 m on each side).
See also
* milli- (inverse of kilo- prefix, denoting a factor of 1/1000)
* kibi- (binary prefix, denoting a factor of 1024)
* RKM code
The RKM code, also referred to as "letter and numeral code for resistance and capacitance values and tolerances", "letter and digit code for resistance and capacitance values and tolerances", or informally as "R notation" is a notation to speci ...
References
{{SI prefixes (infobox)
SI prefixes
1000 (number)
he:תחיליות במערכת היחידות הבינלאומית#קילו