– the intergovernmental organization through which Member States act together
     on matters related to measurement science and measurement standards.
Search facility:


| Site map | News | Contact us | [ FR ]
SI Brochure: The International System of Units (SI) [8th edition, 2006; updated in 2014]
1st CGPM, 1889
Sanction of the international prototypes of the metre and the kilogram
3rd CGPM, 1901
Declaration concerning the definition of the litre
3rd CGPM, 1901
Declaration on the unit of mass and on the definition of weight; conventional value of gn
7th CGPM, 1927
Definition of the metre by the international Prototype
CIPM, 1946
Definition of photometric units
CIPM, 1946
Definitions of electric units
9th CGPM, 1948
Triple point of water; thermodynamic scale with a single fixed point; unit of quantity of heat (joule)
CGPM, 1948
Adoption of "degree Celsius"
9th CGPM, 1948
Proposal for establishing a practical system of units of measurement
9th CGPM, 1948
Writing and printing of unit symbols and of numbers
10th CGPM, 1954
Definition of the thermodynamic temperature scale
10th CGPM, 1954
Definition of the standard atmosphere
10th CGPM, 1954
Practical system of units
CIPM, 1956
Definition of the unit of time (second)
CIPM, 1956
Système International d'Unités
11th CGPM, 1960
Definition of the metre
11th CGPM, 1960
Definition of the unit of time (second)
11th CGPM, 1960
Système International d'Unités
11th CGPM, 1960
Cubic decimetre and litre
CIPM, 1961
Cubic decimetre and litre
CIPM, 1964
Atomic and molecular frequency standards
12th CGPM, 1964
Atomic standard of frequency
12th CGPM, 1964
Litre
12th CGPM, 1964
Curie
12th CGPM, 1964
SI prefixes femto and atto
CIPM, 1967
Decimal multiples and submultiples of the unit of mass
13th CGPM, 1967/68
SI unit of time (second)
13th CGPM, 1967/68
SI unit of thermodynamic temperature (kelvin)
13th CGPM, 1967/68
Definition of the SI unit of thermodynamic temperature (kelvin)
13th CGPM, 1967/68
SI unit of luminous intensity (candela)
13th CGPM, 1967/68
SI derived units
13th CGPM, 1967/68
Abrogation of earlier decisions (micron, new candle)
CIPM, 1969
Système International d'Unités, Rules for application of Resolution 12 of the 11th CGPM (1960)
CCDS, 1970
Definition of TAI
CGPM, 1971
Pascal and siemens
14th CGPM, 1971
International Atomic Time, function of CIPM
14th CGPM, 1971
SI unit of amount of substance (mole)
15th CGPM, 1975
Recommended value for the speed of light
15th CGPM, 1975
Coordinated Universal Time (UTC)
15th CGPM, 1975
SI units for ionizing radiation: becquerel
15th CGPM, 1975
SI units for ionizing radiation: gray
15th CGPM, 1975
SI prefixes peta and exa
16th CGPM, 1979
SI unit of luminous intensity (candela)
16th CGPM, 1979
Special name for the SI unit of dose equivalent (sievert)
16th CGPM, 1979
Symbols for the litre
CIPM, 1980
SI supplementary units (radian and steradian)
17th CGPM, 1983
Definition of the metre
17th CGPM, 1983
On the realization of the definition of the metre
CIPM, 1984
Concerning the sievert
18th CGPM, 1987
Forthcoming adjustment to the representations of the volt and of the ohm
CIPM, 1988
Representation of the volt by means of the Josephson effect
CIPM, 1988
Representation of the ohm by means of the quantum Hall effect
CIPM, 1989
The International Temperature Scale of 1990
19th CGPM, 1991
SI prefixes zetta, zepto, yotta and yocto
20th CGPM, 1995
Elimination of the class of supplementary units in the SI
21st CGPM, 1999
The definition of the kilogram
21st CGPM, 1999
Special name for the SI derived unit mole per second, the katal, for the expression of catalytic activity
CIPM, 2000
"Use of the von Klitzing constant to express the value of a reference standard of resistance as a function of the quantum Hall effect"
CIPM, 2001
"SI units" and "units of the SI"
CIPM, 2002
Revision of the practical realization of the definition of the metre
CIPM, 2002
Dose equivalent
CIPM, 2003
Revision of the Mise en Pratique list of recommended radiations
22nd CGPM, 2003
Symbol for the decimal marker
CIPM, 2005
Clarification of the definition of the kelvin, unit of thermodynamic temperature
CIPM, 2005
Revision of the Mise en pratique list of recommended radiations
CIPM, 2006
Concerning secondary representations of the second
CIPM, 2007
Revision of the Mise en pratique list of recommended radiations
23rd CGPM, 2007
On the revision of the mise en pratique of the definition of the metre and the development of new optical frequency standards
23rd CGPM, 2007
Clarification of the definition of the kelvin, unit of thermodynamic temperature
23rd CGPM, 2007
On the possible redefinition of certain base units of the International System of Units (SI)
CIPM, 2009
Updates to the list of standard frequencies
24th CGPM, 2011
On the possible future revision of the International System of Units, the SI
24th CGPM, 2011
On the revision of the mise en pratique of the metre and the development of new optical frequency standards
CIPM, 2013
Updates to the list of standard frequencies
25th CGPM, 2014
On the future revision of the International System of Units, the SI
CIPM, 2015
Updates to the list of standard frequencies
[Updated 2016]

This appendix lists those decisions of the CGPM and the CIPM that bear directly upon definitions of the units of the SI, prefixes defined for use as part of the SI, and conventions for the writing of unit symbols and numbers. It is not a complete list of CGPM and CIPM decisions. For a complete list, reference must be made to:

Since the SI is not a static convention, but evolves following developments in the science of measurement, some decisions have been abrogated or modified; others have been clarified by additions. In the SI brochure, a number of notes have been added by the BIPM to make the text more understandable; they do not form part of the original text.

The "Chronological list" tab above gives access to the decisions of the CGPM and CIPM in chronological order. In order to make it easy to locate decisions related to particular topics a table of contents is included below, ordered by subject:


Establishment of the SI

Base units of the SI

SI derived and supplementary units

SI derived units:

12th CGPM, 1964 accepts the continued use of the curie as a non-SI unit
13th CGPM, 1967/68 lists some examples of derived units
15th CGPM, 1975 adopts the special names becquerel, Bq, and gray, Gy
16th CGPM, 1979 adopts the special name sievert, Sv
CIPM, 1984 decides to clarify the relationship between absorbed dose (SI unit gray) and dose equivalent (SI unit sievert)
CIPM, 2002 modifies the relationship between absorbed dose and dose equivalent

Supplementary units:

CIPM, 1980 decides to interpret supplementary units as dimensionless derived units
20th CGPM, 1995 decides to abrogate the class of supplementary units, and confirms the CIPM interpretation that they are dimensionless derived units

Terminology and the acceptance of units for use with the SI

SI prefixes:

12th CGPM, 1964 decides to add femto and atto to the list of prefixes
15th CGPM, 1975 decides to add peta and exa to the list of prefixes
19th CGPM, 1991 decides to add zetta, zepto, yotta and yocto to the list of prefixes

Unit symbols and numbers:

9th CGPM, 1948 decides rules for printing unit symbols

Unit names:

13th CGPM, 1967/68 abrogates the use of the micron and new candle as units accepted for use with the SI

The decimal marker:

22nd CGPM, 2003 decides to allow the use of the point or the comma on the line as the decimal marker

Units accepted for use with the SI: an example, the litre:

3rd CGPM, 1901 defines the litre as the volume of 1 kg of water
11th CGPM, 1960 requests the CIPM to report on the difference between the litre and the cubic decimetre
CIPM, 1961 recommends that volume be expressed in SI units and not in litres
12th CGPM, 1964 abrogates the former definition of the litre,
recommends that litre may be used as a special name for the cubic decimetre
16th CGPM, 1979 decides, as an exception, to allow both l and L as symbols for the litre

more details...