Time Department
From navigation and telecommunications to science and digital infrastructure, internationally coordinated time underpins modern life. The BIPM works with time laboratories around the world to make this possible, helping to maintain Coordinated Universal Time (UTC), the international reference time scale.
Keeping the world’s clocks coordinated
The BIPM Time Department computes and disseminates Coordinated Universal Time (UTC) using clock and clock-comparison data contributed by National Metrology Institutes (NMIs) and time laboratories.
Alongside UTC, the Department provides Rapid UTC (UTCr) and TT(BIPM) as complementary time-scale products, supporting the needs of time laboratories and scientific applications and helping maintain accurate and internationally comparable time and frequency measurements.
How international timekeeping works
UTC is built through international cooperation between time laboratories and the BIPM.
Time laboratories
Maintain local realizations of UTC.
Clock data
Clock and time-transfer data are contributed to the BIPM.
BIPM
Computes international reference time scales.
UTC
Provides the international reference for timekeeping.
The world
Navigation, networks, science and society stay synchronized.
Explore the Department’s work
Explore Coordinated Universal Time (UTC) and the complementary time-scale products provided by the BIPM Time Department.
CGPM Resolution 4 addresses the future of UTC.
Optical frequency standards are being evaluated internationally.
Work continues towards a possible redefinition of the second.
Building knowledge and expertise in time metrology
The BIPM supports Member States and Associates in developing the knowledge and technical capabilities needed to contribute to international timekeeping.
UTC Summer Schools
Practical training for laboratories contributing to UTC(k) and UTC.
CBKT activities
Capacity-building activities that support participation in the worldwide coordinated metrological system.
Video explainers
Explore BIPM webinars, expert presentations and explainers on key topics in time and frequency metrology.
Frequently asked questions
Find quick answers about the work of the BIPM Time Department, international time scales and the future of timekeeping.
What does the BIPM Time Department do?
The BIPM Time Department coordinates international contributions to timekeeping and computes and disseminates international reference time scales. It works with National Metrology Institutes (NMIs) and time laboratories worldwide, using clock and time-transfer data contributed by participating laboratories.
Why do we need UTC?
UTC provides a common international reference for time, supporting navigation, telecommunications, digital networks, science and civil time.
What is the difference between UTC, Rapid UTC and TT(BIPM)?
UTC is the international reference for timekeeping and is published monthly. Rapid UTC (UTCr) provides a weekly rapid solution for participating laboratories. TT(BIPM) is a realization of Terrestrial Time calculated retrospectively for scientific applications requiring high long-term stability and accuracy.
How do laboratories contribute to international timekeeping?
Participating National Metrology Institutes (NMIs) and designated time laboratories maintain local time scales and contribute clock and time-transfer data to the BIPM. The BIPM uses these international contributions to compute reference time scales and publishes the results that allow laboratories to compare their local realizations with the international reference.
What is TAI, and how does it relate to UTC?
International Atomic Time (TAI) is a continuous atomic time scale computed by the BIPM from clock data contributed by participating laboratories. UTC has the same rate as TAI but differs from it by an integral number of seconds as a result of the application of leap seconds which are added to maintain strict agreement with the Earth rotation.
How is international timekeeping changing?
International timekeeping continues to evolve as advances in atomic clocks enable increasingly accurate measurements. The international metrology community is preparing for developments including a possible redefinition of the second and changes to the way UTC is maintained, while also considering emerging requirements for timekeeping beyond Earth.
International scientific coordination
Related Consultative Committee
The BIPM works through its Consultative Committees to bring together international expertise and coordinate scientific work in key areas of metrology. For time and frequency, the CCTF provides the international forum for this cooperation, helping to identify priorities and coordinate work across the field.
Explore the BIPM’s other Departments
Discover how the BIPM’s scientific and technical Departments work together to support the worldwide measurement system.
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