——————————————————————————
Bureau International
des Poids et Mesures
The International
System of Units
(SI)
9th edition 2019
————————————————
V3.02
August 2025
,Copyright statement
The SI Brochure is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted
use, distribution, and reproduction in any medium, provided you give appropriate credit to the
original author(s) and the source, provide a link to the Creative Commons license, and indicate
if changes were made.
, The BIPM and the Metre Convention • 117
The BIPM
and the Metre Convention
The International Bureau of Weights and Measures (BIPM) was set up by the Metre
Convention signed in Paris on 20 May 1875 by seventeen States during the final session of
the diplomatic Conference of the Metre. This Convention was amended in 1921.
The BIPM has its headquarters near Paris, in the grounds (43 520 m2) of the Pavillon de
Breteuil (Parc de Saint-Cloud) placed at its disposal by the French Government; its upkeep
is financed jointly by the Member States of the Metre Convention.
The task of the BIPM is to ensure worldwide unification of measurements; its objectives are
to:
• represent the world-wide measurement community, aiming to maximize its uptake and
impact,
• be a centre for scientific and technical collaboration between Member States, providing
capabilities for international measurement comparisons on a shared-cost basis,
• be the coordinator of the world-wide measurement system, ensuring it gives comparable
and internationally accepted measurement results.
The BIPM operates under the exclusive supervision of the International Committee for
Weights and Measures (CIPM) which itself comes under the authority of the General
Conference on Weights and Measures (CGPM) and reports to it on the work accomplished
by the BIPM.
Delegates from all Member States attend the General Conference, which normally meets
every four years. The function of these meetings is to:
• discuss and initiate the arrangements required to ensure the propagation and
improvement of the International System of Units (SI), which is the modern form of the
metric system;
• confirm the results of new fundamental metrological determinations and various
scientific resolutions of international scope;
• take all major decisions concerning the finance, organization and development of the
BIPM.
The CIPM has eighteen members each from a different State: at present, it meets every year.
The officers of this committee present an annual report on the administrative and financial
position of the BIPM to the Governments of the Member States. The principal task of the
CIPM is to ensure worldwide uniformity in units of measurement. It does this by direct action
or by submitting proposals to the CGPM.
, 118 • The BIPM and the Metre Convention
The activities of the BIPM, which in the beginning were limited to measurements of length
and mass, and to metrological studies in relation to these quantities, have been extended to
standards of measurement of electricity (1927), photometry and radiometry (1937), ionizing
radiation (1960), time scales (1988) and to chemistry (2000). To this end the original
laboratories, built in 1876 -1878, were enlarged in 1929; new buildings were constructed in
1963-1964 for the ionizing radiation laboratories, in 1984 for the laser work and in 1988 for
a library and offices. In 2001 a new building for the workshop, offices and meeting rooms
was opened.
Some forty-five physicists and technicians work in the BIPM laboratories. They mainly
conduct metrological research, international comparisons of realizations of units and
calibrations of standards. An annual Director’s report gives details of the work in progress.
Following the extension of the work entrusted to the BIPM in 1927, the CIPM has set up
bodies, known as Consultative Committees, whose function is to provide it with information
on matters that it refers to them for study and advice. These Consultative Committees, which
may form temporary or permanent working groups to study special topics, are responsible
for coordinating the international work carried out in their respective fields and for proposing
recommendations to the CIPM concerning units.
The Consultative Committees have common regulations (Document CIPM-D-01, Rules of
procedure for the Consultative Committees (CCs) created by the CIPM, CC working groups
and CC workshops). They meet at irregular intervals. The president of each Consultative
Committee is designated by the CIPM and is normally a member of the CIPM. The members
of the Consultative Committees are metrology laboratories and specialized institutes, agreed
by the CIPM, which send delegates of their choice. In addition, there are individual members
appointed by the CIPM, and a representative of the BIPM (Document CIPM-D-01, Rules of
procedure for the Consultative Committees (CCs) created by the CIPM, CC working groups
and CC workshops). At present, there are ten such committees:
1. The Consultative Committee for Electricity and Magnetism (CCEM), new name given
in 1997 to the Consultative Committee for Electricity (CCE) set up in 1927;
2. The Consultative Committee for Photometry and Radiometry (CCPR), new name given
in 1971 to the Consultative Committee for Photometry (CCP) set up in 1933 (between
1930 and 1933 the CCE dealt with matters concerning photometry);
3. The Consultative Committee for Thermometry (CCT), set up in 1937;
4. The Consultative Committee for Length (CCL), new name given in 1997 to the
Consultative Committee for the Definition of the Metre (CCDM), set up in 1952;
5. The Consultative Committee for Time and Frequency (CCTF), new name given in 1997
to the Consultative Committee for the Definition of the Second (CCDS) set up in 1956;
6. The Consultative Committee for Ionizing Radiation (CCRI), new name given in 1997 to
the Consultative Committee for Standards of Ionizing Radiation (CCEMRI) set up in
1958 (in 1969 this committee established four sections: Section I (X- and γ-rays,
electrons), Section II (Measurement of radionuclides), Section III (Neutron
measurements), Section IV (α-energy standards); in 1975 this last section was dissolved
and Section II was made responsible for its field of activity);
7. The Consultative Committee for Units (CCU), set up in 1964 (this committee replaced
the Commission for the System of Units set up by the CIPM in 1954);
Bureau International
des Poids et Mesures
The International
System of Units
(SI)
9th edition 2019
————————————————
V3.02
August 2025
,Copyright statement
The SI Brochure is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted
use, distribution, and reproduction in any medium, provided you give appropriate credit to the
original author(s) and the source, provide a link to the Creative Commons license, and indicate
if changes were made.
, The BIPM and the Metre Convention • 117
The BIPM
and the Metre Convention
The International Bureau of Weights and Measures (BIPM) was set up by the Metre
Convention signed in Paris on 20 May 1875 by seventeen States during the final session of
the diplomatic Conference of the Metre. This Convention was amended in 1921.
The BIPM has its headquarters near Paris, in the grounds (43 520 m2) of the Pavillon de
Breteuil (Parc de Saint-Cloud) placed at its disposal by the French Government; its upkeep
is financed jointly by the Member States of the Metre Convention.
The task of the BIPM is to ensure worldwide unification of measurements; its objectives are
to:
• represent the world-wide measurement community, aiming to maximize its uptake and
impact,
• be a centre for scientific and technical collaboration between Member States, providing
capabilities for international measurement comparisons on a shared-cost basis,
• be the coordinator of the world-wide measurement system, ensuring it gives comparable
and internationally accepted measurement results.
The BIPM operates under the exclusive supervision of the International Committee for
Weights and Measures (CIPM) which itself comes under the authority of the General
Conference on Weights and Measures (CGPM) and reports to it on the work accomplished
by the BIPM.
Delegates from all Member States attend the General Conference, which normally meets
every four years. The function of these meetings is to:
• discuss and initiate the arrangements required to ensure the propagation and
improvement of the International System of Units (SI), which is the modern form of the
metric system;
• confirm the results of new fundamental metrological determinations and various
scientific resolutions of international scope;
• take all major decisions concerning the finance, organization and development of the
BIPM.
The CIPM has eighteen members each from a different State: at present, it meets every year.
The officers of this committee present an annual report on the administrative and financial
position of the BIPM to the Governments of the Member States. The principal task of the
CIPM is to ensure worldwide uniformity in units of measurement. It does this by direct action
or by submitting proposals to the CGPM.
, 118 • The BIPM and the Metre Convention
The activities of the BIPM, which in the beginning were limited to measurements of length
and mass, and to metrological studies in relation to these quantities, have been extended to
standards of measurement of electricity (1927), photometry and radiometry (1937), ionizing
radiation (1960), time scales (1988) and to chemistry (2000). To this end the original
laboratories, built in 1876 -1878, were enlarged in 1929; new buildings were constructed in
1963-1964 for the ionizing radiation laboratories, in 1984 for the laser work and in 1988 for
a library and offices. In 2001 a new building for the workshop, offices and meeting rooms
was opened.
Some forty-five physicists and technicians work in the BIPM laboratories. They mainly
conduct metrological research, international comparisons of realizations of units and
calibrations of standards. An annual Director’s report gives details of the work in progress.
Following the extension of the work entrusted to the BIPM in 1927, the CIPM has set up
bodies, known as Consultative Committees, whose function is to provide it with information
on matters that it refers to them for study and advice. These Consultative Committees, which
may form temporary or permanent working groups to study special topics, are responsible
for coordinating the international work carried out in their respective fields and for proposing
recommendations to the CIPM concerning units.
The Consultative Committees have common regulations (Document CIPM-D-01, Rules of
procedure for the Consultative Committees (CCs) created by the CIPM, CC working groups
and CC workshops). They meet at irregular intervals. The president of each Consultative
Committee is designated by the CIPM and is normally a member of the CIPM. The members
of the Consultative Committees are metrology laboratories and specialized institutes, agreed
by the CIPM, which send delegates of their choice. In addition, there are individual members
appointed by the CIPM, and a representative of the BIPM (Document CIPM-D-01, Rules of
procedure for the Consultative Committees (CCs) created by the CIPM, CC working groups
and CC workshops). At present, there are ten such committees:
1. The Consultative Committee for Electricity and Magnetism (CCEM), new name given
in 1997 to the Consultative Committee for Electricity (CCE) set up in 1927;
2. The Consultative Committee for Photometry and Radiometry (CCPR), new name given
in 1971 to the Consultative Committee for Photometry (CCP) set up in 1933 (between
1930 and 1933 the CCE dealt with matters concerning photometry);
3. The Consultative Committee for Thermometry (CCT), set up in 1937;
4. The Consultative Committee for Length (CCL), new name given in 1997 to the
Consultative Committee for the Definition of the Metre (CCDM), set up in 1952;
5. The Consultative Committee for Time and Frequency (CCTF), new name given in 1997
to the Consultative Committee for the Definition of the Second (CCDS) set up in 1956;
6. The Consultative Committee for Ionizing Radiation (CCRI), new name given in 1997 to
the Consultative Committee for Standards of Ionizing Radiation (CCEMRI) set up in
1958 (in 1969 this committee established four sections: Section I (X- and γ-rays,
electrons), Section II (Measurement of radionuclides), Section III (Neutron
measurements), Section IV (α-energy standards); in 1975 this last section was dissolved
and Section II was made responsible for its field of activity);
7. The Consultative Committee for Units (CCU), set up in 1964 (this committee replaced
the Commission for the System of Units set up by the CIPM in 1954);
