Sharing Practical Expertise: 2025 Kibble Balance Technical Meeting
As countries continue to refine the realization of the kilogram and expand applications of precision mass measurement, the Kibble balance remains one of the most important instruments in modern metrology. From realizing the SI kilogram to supporting new approaches to force, torque and industrial mass measurements, progress in Kibble balance technology directly shapes international capabilities in measurement science.
The BIPM has had its own Kibble balance since 2005 and it is one of the four Kibble balances which participated in all three key comparisons of kilogram realizations, from 2019 to 2024.
Against this backdrop, the 2025 Kibble Balance Technical Meeting (KBTM) was held at the BIPM from 18 to 20 November, bringing together experts to exchange updates, discuss new developments and—this year—share practical knowledge with the next generation of researchers.
Photo caption: Panellists during the KBTM Special Session – Knowledge Transfer on Kibble Balance Core Topics, and participants visiting the BIPM’s Kibble Balance lab. Copyright ©BIPM.
Over the first two days, the programme covered a wide range of technical topics central to current Kibble balance work, including:
- NMI-level Kibble balances for realizing the kilogram
- participation in the key comparison of realization experiments (CCM.M-K8)
- table-top balances for smaller mass ranges
- developments in mass, force and torque for industrial applications
These discussions brought together progress updates from institutes worldwide, providing valuable insight into the evolving capabilities of national Kibble balance programmes.
New in 2025: Special Session on Knowledge Transfer
For the first time, the meeting included a special Knowledge Transfer Session on Day 3. Six invited experts presented an overview of core topics in Kibble balance technology, offering structured guidance for NMIs and research groups entering or expanding this field.
The talks covered both foundational and specialised areas, including general considerations for building a Kibble balance, magnetic circuits, electrical measurements, mechanics and alignment, optical sensors and data synchronisation, and mass and gravity.
This session provided a unique opportunity for early-career metrologists, university researchers and new entrants to the field to engage directly with leading experts.
Key sessions:
- 0:00 – Introduction to the KBTM Special Session
- 0:02:40 – General considerations for building a Kibble balance – Ian Robinson (NPL)
- 0:26:38 – Optical sensors and data synchronization – Franck Bielsa (BIPM)
- 1:02:24 – Magnet/coil design and effects – Shisong Li (Tsinghua University)
- 1:44:46 – Mass and gravity – Richard Green (NRC)
- 2:17:35 – Mechanism and alignment – Darine Haddad (NIST)
- 2:41:38 – Electrical measurements – Ian Robinson (NPL)
A Strong Turnout and Growing Community
The 2025 KBTM attracted around 60 in-person participants, with more than 20 online attendees joining for the knowledge-transfer programme. Participants represented National Metrology Institutes (NMIs) and university research groups working on precision mass measurements and related technologies.
The high level of engagement reflects the continued importance of the Kibble balance to global metrology — both for maintaining the SI kilogram and for enabling new measurement capabilities across science and industry.
Photo caption: Group photo of participants at the 2025 Kibble Balance Technical Meeting (KBTM), held at the BIPM headquarters on 20 November 2025. ©BIPM.
Key Terms Explained
The KBTM was launched over 20 years ago and serves as a dedicated forum for reporting progress and exchanging ideas on Kibble balance research. The bi-annual meeting is organized by institutes actively developing Kibble balances, and provides a platform to review advances, troubleshoot experimental challenges and foster international cooperation.
This year, hosting the meeting at the BIPM marked a special milestone:
- 150 years since the signing of the Metre Convention, and
- 50 years since the invention of the Kibble balance by Bryan Kibble.
Originally named the watt balance, the instrument was later renamed in honour of its inventor. This was the second time the BIPM has hosted the meeting—the first being in 2007.
A Kibble balance is an instrument used to realize the SI unit of mass by linking mechanical power to electrical power and using quantum electrical standards. Learn more.
CCM.M-K8 is the key comparison of realization experiments for the kilogram, organised under the Consultative Committee for Mass and Related Quantities (CCM). It evaluates consistency between national realizations of the SI kilogram. Learn more.