The stature of the human body, according to the Talmudists, contains about 3 cubits from the feet to the head. Now the ordinary stature of men, when they are barefoot, is greater than 5 Roman feet and less than 6 Roman feet. Take a third part of this and the vulgar cubit will be more than 20 unicae and less than 24 unicae of the Roman foot; and consequently the Sacred Cubit will be more than 24 unicae and less than 28 + (4/5) unicae of the same foot. Sir Isaac Newton

Although standardization of weights and measures has been a goal of social and economic advance since very early times, it was not until the 18th century that there was a unified system of measurement. The earliest systems of weights and measures were based on human morphology. The names of units often referred to parts of the body: the inch or pouce, the hand, the foot, and the yard or cubit corresponded to dimensions of the human body. Consequently, these units of measurement were not fixed; they varied from one town to another, from one occupation to another, and on the type of object to be measured.

This lack of a standardized system of measurements was a source of error and fraud in commercial and social transactions, putting a brake on international commerce and prevented the development of science as an international endeavour. With the expansion of industry and trade, there was an increasing need for harmonization of weights and measures between countries. Politicians and scientists resolved this situation by adopting a standard of measurement (distance or weight) by comparison with a standard (étalon) taken from Nature.

One of the first such natural measures was the metre, which was defined in a decree of the French National Assembly (7 April 1795) as being equal to the ten millionth part of one quarter of the terrestrial meridian, but specified by measurements undertaken between Dunkerque and Barcelona. Such a unit was not arbitrary, being based on the size of the Earth. Once the base unit of length had been decided upon, it was possible to establish the resulting units of measure: the square metre (for area) and the cubic metre (for volume). The kilogram was originally defined as the weight of a certain volume of water, a convenient and readily purified liquid.

Such a system of simple multiples of base units lends itself naturally to extension. The decimal metric system was introduced in France on 7 April 1795 by the law "On weights and measures". This caused a major change in the everyday life of ordinary people, readily allowing the calculation of, for example, areas and volumes. Conversion from a sub-multiple to a multiple unit of length simply consists of moving the decimal marker – two or three places for area or volume, respectively.

The first standards (étalons) of the metre and the kilogram, against which all future copies were to be compared, were deposited in the Archives of the French Republic in 1799, dedicated to "all men and all times".

Because of its simplicity and universality, the decimal metric system spread rapidly outside France. The development of railways, the growth of industry and the increasing importance of social and economic exchange all required accurate and reliable units of measurement. Adopted at the start of the 19th century in several Italian provinces, the metric system became compulsory in the Netherlands from 1816 and was chosen by Spain in 1849. In France, the decimal metric system was exclusively adopted with the law of 4 July 1837.

After 1860, the countries of Latin America took up the metre, and there was a steady increase in the adoption of the metric system by other nations during the latter half of the nineteenth century (for example, the United States of America, 1866, Canada, 1871, Germany, 1871). However, these countries were dependent for their national standards on copies of the original prototypes. This dependence, together with the lack of uniformity in making copies, limited the desired international standardization. To overcome these difficulties, the Bureau International des Poids et Mesures (BIPM) was founded by the terms of the diplomatic treaty known as the Metre Convention on 20 May 1875. To celebrate the signing of the Metre Convention, the date of 20 May is known as World Metrology Day.