Editing Base unit of measurement (section)

{{Short description|Unit of measurement adopted by convention for a base quantity}}
{{about|the type of unit of measure|the concept in number theory|Fundamental unit (number theory)}}
{{refimprove|date=March 2013}}

A '''base unit of measurement''' (also referred to as a '''base unit''' or '''fundamental unit''') is a [[unit of measurement]] adopted for a ''[[base quantity]]''. A base quantity is one of a conventionally chosen subset of [[physical quantity|physical quantities]], where no quantity in the subset can be expressed in terms of the others. The [[SI base units]], or ''Systéme International d'unités'', consists of the metre, kilogram, second, ampere, kelvin, mole and candela.

A '''unit multiple''' (or '''multiple of a unit''') is an integer [[multiple (mathematics)|multiple]] of a given unit; likewise a '''unit submultiple''' (or '''submultiple of a unit''') is a [[submultiple]] or a [[unit fraction]] of a given unit.<ref name=80000-1:2009>{{cite web|title=ISO 80000-1:2009|url=https://www.iso.org/standard/30669.html|publisher=[[International Organization for Standardization]]|access-date=2019-09-15|archive-date=2019-07-02|archive-url=https://web.archive.org/web/20190702201943/https://www.iso.org/standard/30669.html|url-status=live}}</ref> 
''[[Unit prefix]]es'' are common base-10 or base-2 powers multiples and submultiples of units.

While a base unit is one that has been explicitly so designated,<ref>
{{cite book
 |title = The International System of Units (SI)
 |url = https://archive.org/details/internationalsys3309tayl
 |at = p. 56 (10th CGPM, 1954, Resolution 6)
 |first1 = Barry N.
 |last1 = Taylor
 |first2 = Ambler
 |last2 = Thompson
 |year = 2008
 |publisher = U.S. Department of Commerce
 |location = Washington, D.C.
}}</ref> 
a '''derived unit''' is unit for a ''[[derived quantity]]'', involving the combination of quantities with different units;<ref name=80000-1:2009/> several ''[[SI derived units]]'' are specially named.
A ''[[coherent derived unit]]'' involves no [[conversion factor]]s.