The International System of Units
The International System of Units (SI) is the globally recognised standard for comparable measurements. It defines seven base units on which all physical quantities are based. METAS ensures that the SI units can be correctly realised and applied in Switzerland.
The role of METAS
The International System of Units (Système international d'unités, SI) was introduced in 1960 by the General Conference on Weights and Measures (Conférence Générale des Poids et Mesures, CGPM). Since the fundamental revision of 2019, all SI units have been based on defined physical constants.
As the national metrology institute, METAS ensures that the base units are correctly realised in Switzerland and are metrologically traceable to the SI units. In doing so, it lays the foundation for reliable measurements in research, industry and everyday life.
The seven SI base units
The table below provides an overview of the SI base units and the constants by which they are defined:
Review of SI
The fundamental revision of the SI was implemented in 2019. Since then, all units have been defined in terms of physical constants.
The last physical artefact – the prototype kilogram – has therefore been decommissioned. The ampere, the kelvin and the mole are now also based on fixed constants.
The new, updated SI is stable, uniform worldwide and enables more accurate measurements and technological innovations in the long term.
More information
Short information about the proposed revision of the SI (PDF, 72 kB, 06.07.2020) International system of units SI