Mise en œuvre de la troisième valeur de consensus du kilogramme à partir du 1er mars 2026
From 1 March 2026, the international metrology community will implement the third Consensus Value of the kilogram, following completion of the third key comparison of kilogram realizations, organized by the BIPM in 2025.
This third Consensus Value will allow us to maintain internationally consistent and traceable mass measurements while independent realizations of the kilogram continue to develop.
The Third Consensus Value
Based on the results of the last three key comparisons, the new Consensus Adjustment corresponds to 1 kg − 12 µg. This represents a change of 5 µg — relative to the second Consensus Adjustment — and a cumulative difference of 12 µg — with respect to traceability to the previous definition of the kilogram. The standard uncertainty of the Consensus Value remains unchanged at 20 µg.
As a result of these findings, mass values traceable to the second Consensus Value must be reduced by 5 µg, while those traceable to the previous IPK-based definition must be reduced by 12 µg.
Graph caption: This graph depicts differences observed during the third key comparison between mass values attributed by the National Metrology Institutes (NMIs) to a nominal 1 kg mass and related standard uncertainties.
Ten institutes participated in the third key comparison, conducted between September 2024 and December 2025: The BIPM, LNE (France), METAS (Switzerland), NIST (USA), NRC (Canada) and UME (Türkiye) operating Kibble balances; NIM (China) using a joule balance; and NMIJ (Japan), PTB (Germany) and CMS-ITRI (Chinese Taipei) using 28Si spheres measured by the X-ray Crystal Density (XRCD) method.
The full report is available on the BIPM website here.
Background
Since 20 May 2019, the kilogram has been defined by fixing the numerical value of the Planck constant. Realizations are currently achieved using Kibble balances and the X-ray Crystal Density (XRCD) method.
Until agreement between independent realizations is considered satisfactory for ensuring internationally consistent measurements of mass, the Consultative Committee for Mass and Related Quantities (CCM) coordinates dissemination of the kilogram through a Consensus Value.
The third Consensus Value, to be implemented on 1 March 2026, represents the next step in maintaining internationally consistent measurements of mass under the revised SI during this phase of implementation.
Key terms and concepts explained
Consensus Value of the kilogram: Representation of the SI unit kilogram, based on an aggregate of measurements from the global ensemble of realization experiments, that can determine mass from the Planck constant. It is the global realization of the SI kg.
Consensus Adjustment of the kilogram: An adjustment to the global mass scale, implemented periodically in response to changes in measurements from the global ensemble of realization experiments. It is expressed as a cumulative change since the previous definition of the kilogram.
Kibble balance: A device which compares the weight of a mass standard to a known electromagnetic force which depends on the Planck constant through electrical quantum standards.
X-ray crystal density method: A method which determines the mass of a nearly perfect sphere of isotopically-enriched monocrystalline silicon by summing the masses of all atoms it contains; the masses of the atoms being determined using the Planck constant.