History of the Metric System Timeline

The Netherlands became one of the first countries outside France to adopt the metric system, following its annexation experience under Napoleon.

Image source: Metrication

Belgium adopted the metric system shortly after gaining independence, following the Dutch precedent established during the Napoleonic era.

Spain passed legislation adopting the metric system, becoming one of the early adopters on the European continent outside France.

Portugal officially adopted the metric system, replacing its traditional Portuguese units with standard metric measurements.

Following Italian unification, the newly formed Kingdom of Italy adopted the metric system nationwide, unifying diverse regional measurement traditions.

Image source: Italian units of measurement

Brazil adopted the metric system by imperial law, becoming one of the first countries in the Americas to do so.

The United States Congress passed the Metric Act, making it lawful to use the metric system throughout the country, though it did not mandate adoption.

Image source: Metric Act of 1866

The North German Confederation adopted the metric system, which was carried over into the German Empire upon its founding in 1871.

Image source: Metrication

The young Soviet government decreed the adoption of the metric system, completing full implementation by 1927 and replacing traditional Russian units.

Japan enacted laws mandating the use of the metric system, though traditional shakkanhō units remained in parallel use for decades afterward.

The British government announced a policy of voluntary metrication, beginning a gradual transition from imperial units that continues in various sectors today.

Image source: Metrication in the United Kingdom

Australia undertook a swift and successful metrication program, converting road signs, trade, education, and weather reporting to metric units within about two decades.

Image source: Metrication in Australia

Canada launched its Metric Commission in 1971 to convert the country to the metric system, largely completing the transition across industry and commerce by the mid-1980s.

Image source: Metrication in Canada

The US Department of Commerce published the three-volume 'A Metric America' report recommending a coordinated national transition to the metric system.

Image source: Metrication in the United States

President Gerald Ford signed the Metric Conversion Act, declaring metric the preferred system of weights and measures in the United States, though conversion remained voluntary.

EU directives required metric-only or dual labelling of packaged goods across member states, reinforcing the metric system as Europe's common commercial standard.

Image source: European units of measurement directives

The First International Statistical Congress in Brussels recommended the adoption of a single decimal system of weights and measures for international statistical comparisons.

Image source: First International Statistical Congress

The British Association for the Advancement of Science formalized the centimetre-gram-second (CGS) system, extending metric units into electromagnetism and physics research.

The International Committee for Weights and Measures was created to supervise the BIPM and provide scientific oversight between meetings of the CGPM.

Image source: International Bureau of Weights and Measures

The BIPM was established at Sèvres, near Paris, to safeguard international prototype standards of the metre and kilogram and coordinate metrology worldwide.

Seventeen nations signed the Metre Convention in Paris, establishing permanent international institutions to maintain and refine the metric standards.

Image source: Metre Convention

The CGPM sanctioned the International Prototype Metre and Kilogram, distributing copies to member states and formalizing global metric standards.

The third CGPM defined the litre as the volume of one kilogram of water at maximum density, resolving ambiguities in the relationship between mass and volume units.

Image source: Litre

The scope of the Metre Convention was extended to electrical units, and subsequent conferences defined the ampere, volt, and ohm within the metric framework.

Image source: Ampere

The metre-kilogram-second (MKS) system gained official recognition when the CGPM adopted the ampere as a base unit, forming the MKSA system that preceded SI.

The eleventh CGPM formally established the International System of Units (SI), a modernized, coherent form of the metric system with six base units, later expanded to seven.

Image source: International System of Units

The seventeenth CGPM redefined the metre as the distance light travels in vacuum in 1/299,792,458 of a second, fixing the speed of light exactly and ending dependence on physical artefacts.

The twenty-sixth CGPM voted to redefine the kilogram using Planck's constant, along with revised definitions of the ampere, kelvin, and mole, eliminating the last physical artefact standard.

Image source: 2019 revision of the SI

On World Metrology Day, all SI base units became defined by fundamental physical constants, marking the culmination of over two centuries of refinement of the metric system.