THE METRE CONVENTION – THE PATH TOWARDS A UNIVERSAL LANGUAGE OF MEASUREMENT

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By the end of the 18th century, it became clear that the world needed a common language of measurement. The metre and the kilogram, created in the wake of the French Revolution, paved the way for an international system of units that still unites science, industry, and everyday life.

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In 18th-century France, measurement was in chaos: there were about 800 different units, each with hundreds of local variations—adding up to as many as 250,000 individual measures. This complicated trade, construction, and scientific work.

(Visual 1: Map of regions in France / Source: Public domain)

(Visual 2: Table of non-standardised French units / Source: littlegun.info – Technique: anciennes mesures françaises, October 2025)

 

In 1790, the French Academy of Sciences gathered leading scientists to create a universal system of units. They defined the metre as one ten-millionth of the meridian from the North Pole to the Equator, and the kilogram as the mass of 1 dm³ of water at its maximum density (+4 °C). The first prototypes of both units were made in 1799.

(Visual 3: First metre prototype – “Paris metre” / Source: Public domain)

(Visual 4: First kilogram prototype / Source: Public domain)

 

As the metric system spread across Europe and the world, the need for international agreement grew. This was achieved on 20 May 1875 in Paris, when 17 states signed the Metre Convention, founding the General Conference on Weights and Measures (CGPM) and the International Bureau of Weights and Measures (BIPM). The signatories were: Argentina, Austria-Hungary (including Croatia), Belgium, Brazil, Denmark, France, Germany, Italy, Peru, Portugal, Russia, Spain, Sweden-Norway, Switzerland, Turkey, the United Kingdom, and the United States.

(Visual 5: Title page of the Metre Convention / Source: Documents diplomatiques de la Conférence du Mètre, Paris 1875, Bibliothèque nationale de France, Gallica)

(Visual 6: Measuring units – for all time, for all peoples / Source: Public domain)

 

Interestingly, under Ban Ivan Mažuranić, the Croatian Parliament adopted a separate decision to introduce the metre. In this way, Croatia actively participated in the creation of the global measurement system from the very beginning—not merely as a passive member of Austria-Hungary.

(Visual 7: Ivan Mažuranić, lithograph, ca. 1860 / Source: Wien Museum, Portrait Collection, Author: Josef Anton Bauer)

 

At the historic 2018 CGPM meeting, all seven base SI units—metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd)—were redefined using fundamental constants of nature. On 20 May 2019, the 144th anniversary of the Metre Convention, the newly defined International System of Units (SI) became official.

(Visual 8: Symbolic representation of the seven SI base units with associated constants / Source: Public domain)

 

Due to its historical and cultural significance, World Metrology Day—20 May—has been celebrated worldwide since 2024 as an official UNESCO day, honouring the common language of measurement that the Metre Convention gifted to humanity.

(Visual 9: World Metrology Day 2025 poster / Source: BIPM & OIML)