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Metric prefixes have also been used with some non-metric units. The SI prefixes are metric prefixes that were standardised for use in the International System of Units (SI) by the International Bureau of Weights and Measures (BIPM) in resolutions dating from 1960 to 2022. [1] [2] Since 2009, they have formed part of the ISO/IEC 80000 standard.
For example, the coherent derived SI unit of velocity is the metre per second, with the symbol m/s. [1]: 139 The base and coherent derived units of the SI together form a coherent system of units (the set of coherent SI units). A useful property of a coherent system is that when the numerical values of physical quantities are expressed in terms ...
A number of different units (some only of historical interest) are shown and expressed in terms of the corresponding SI unit. Conversions between units in the metric system are defined by their prefixes (for example, 1 kilogram = 1000 grams, 1 milligram = 0.001 grams) and are thus not listed in this article.
The first group of metric units are those that are at present defined as units within the International System of Units (SI). In its most restrictive interpretation, this is what may be meant when the term metric unit is used. The unit one (1) is the unit of a quantity of dimension one. It is the neutral element of any system of units. [2]
The prefixes of the metric system precede a basic unit of measure to indicate a decadic multiple and fraction of a unit. Each prefix has a unique symbol that is added to the beginning of the unit symbol. Some of the prefixes date back to the introduction of the metric system in the 1790s, but new prefixes have been added, and some have been ...
In the SI system and generally in older metric systems, multiples and fractions of a unit can be described via a prefix on a unit name that implies a decimal (base-10), multiplicative factor. The only exceptions are for the SI-accepted units of time (minute and hour) and angle (degree, arcminute, arcsecond) which, based on ancient convention ...
Conversion of units is the conversion of the unit of measurement in which a quantity is expressed, typically through a multiplicative conversion factor that changes the unit without changing the quantity. This is also often loosely taken to include replacement of a quantity with a corresponding quantity that describes the same physical property.
Unit system Domain Derivation Unit name Unit symbol Dimension symbol Quantity name Definition In SI base units In other SI units SI: Physics: Basic: second [n 1] s: T: time: The duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. s: SI ...