When was the metric system developed?

Metric system of units


The Metric system of units, also briefly Metric system called, is a system of units based on the meter. With its help, the aim was to overcome the confusing variety of different lengths and weights. This goal has also been achieved almost all over the world, with the exception of a few countries such as the USA, in which the Anglo-American system of measurement still prevails.

In physics, the CGS system was initially used, a system of measurement with the basic units Zcentimeter, Gram and S.ekunde. Later (1889) the MKS system was introduced, a system of measurements with the basic units M.eter, Kilogram and S.ekunde, which has been used since 1960 as the International System of Units (Système International d'Unités) is common.


The international standardization of the system of units prevents misunderstandings when dealing with sizes and units and makes size values ​​directly and precisely comparable. This is important for science and technology as well as for industry and trade and thus has a positive effect on society.

A uniform and self-contained, i.e. consistent system of units is of great use for both international and domestic scientific and economic exchange, for example to avoid error-prone conversions and misunderstandings due to ambiguous information. In the area of ​​what would later become the German Empire, around 300 different surface dimensions existed until 1870. Units with the same name were or are different. For example, the German horsepower (PS) is not the same as the British horsepower (HP), and for a mile, different definitions existed for centuries in the various areas of application and regions. A wide variety of scales were used to measure temperatures.


See also:History of weights and measures, Section: The metric system

In China and parts of India there were decimal systems already in ancient times. Proposals to create a purely decimal system of measurement have existed in modern Europe since around the end of the 16th century. Until the end of the 18th century, however, the old systems of measurement, which were based on highly complex numbers, were preferred. However, these were neither international nor value systems. However, modern economics and administration made both considerations desirable for increasing efficiency. That is why the decimal metric system was introduced in revolutionary France under the bourgeois reign of terror on August 1, 1793 in the National Convention.

In the 19th century z. E.g. in the Confederation of Rhine only preparations were made for the introduction of the French decimal system, for example by decimalizing the respective local or a round e.g. 30 cm foot measurement. Only towards the end of the 19th century did the decimal metric system gradually gain acceptance internationally. The Meter Convention was signed in Paris on May 20, 1875, a diplomatic treaty among the 17 leading industrial nations, which agreed on uniform standards for the most important sizes. Without this measure, the further development of the industrialized world might have been impossible, because nationally different units would have made international trade and scientific and technical exchange extremely difficult. The meter convention is still valid and is the basis of the International System of Units (SI). The international organization “Bureau International des Poids et Mesures” (BIPM) was commissioned to maintain the standards laid down in the Meter Convention.

In 1874, the coherent CGS system with three base units, derived units and the prefixes micro to mega was established in Great Britain. Since the previous units had proven to be too complicated, additional “practical units” were introduced in 1880 for the fields of electricity and magnetism, including ohms, volts and amperes.

At the first CGPM in 1889, meters, kilograms and seconds were defined as the international base units (MKS system). The new prototypes for the meter and the kilogram have been approved and distributed to the member states. The so-called international meter prototype replaced the original meter from 1799. The original kilogram (also known as the international kilogram prototype) is still valid. Both are kept in a BIPM vault in Sèvres near Paris.

The International Electrical Congress in Chicago in 1893 introduced units for voltage and resistance called "international". The 1908 International Conference in London confirmed the "international" units of volt and ohm.

In 1946 the ampere was finally added as a further base unit (MKSA system), and in 1954 Kelvin and Candela followed. In 1971 the mole was decided as the last basic unit for the time being. The following overview shows examples of the definitions by which today's SI base units were established in the past:

Size value Previous definitions by the CGPM
1 m 1791/1795/1799, French Parliament: ten millionth part of a quarter of the meridian crossing France.
1960: length which equals 1,650,763.73 wavelengths of the radiation in a vacuum that corresponds to the transition between levels 2p10 and 5d5 of the krypton-86 atom.
since 1983: Distance that light travels in a vacuum in a time of 1/299 792 458 seconds.
1 s earlier: 1 / (86 400) th part of the mean sunny day;
1960: 1 / (31 556 925.9747) th part of the tropical year for January 0, 1900 (= December 31, 1899), 12 o'clock ephemeris time.
today: The radiation corresponding to 9 192 631 770 times the period of the transition between the two hyperfine levels of the ground state of atoms of the nuclide 133Cs.
1 K 1954: [T] = 1 ° K (degrees Kelvin, degrees absolute)
1968: [T] = 1 K (Kelvin) is the 273.16th part of the thermodynamic temperature of the triple point of water.
1 cd 1946/48: Light intensity perpendicular to a 1/6 square centimeter surface of a black body at the temperature of freezing platinum at a pressure of 101,325 Newtons per square meter.

Introduction of the metric system

The introduction of the metric system began in France in the 1790s. The introduction was temporarily reversed. However, the radical changeover of the times and the calendar to a decimal system did not take hold (among other things, a week should consist of ten days).

In the 19th century, the metric system was introduced in most European countries: in the Netherlands, Belgium and Luxembourg in 1820, in Switzerland from 1835, in Spain in the 1850s, in Italy in 1861, in Germany in 1870, in Austria in 1871 and finally in 1907 in Denmark. The United Kingdom is the last European country in the process of conversion; in Ireland it was completed on January 20, 2005 with the conversion of road signs. In the English-speaking world, the introduction is referred to as “metrication” or “metrification”.[1]

Today the metric system is used in almost all countries. Only the USA as well as Myanmar and Liberia have not yet made it mandatory, although in practice it is used by the latter two.[2]

Resistance to adoption, mostly for traditional or aesthetic reasons, has or is essentially only in the US, UK, Canada and Japan. Relics of old systems can be found in many countries, partly in the form of redefined ("metrified") units (e.g. pounds to 500 g) and partly due to the influence of the US economy customs (e.g. for screen size specifications). However, US federal authorities usually require the use of the metric system when awarding contracts (e.g. when technical documents have to be submitted for tenders).

See also


  1. Metrication - Article on “Metrization”, in the English-language Wikipedia
  2. The World Factbook, Central Intelligence Agency, Appendix G. https://www.cia.gov/library/publications/the-world-factbook/appendix/appendix-g.html

Category: System of sizes and units