page_title: Metrication in the United Kingdom
section_title: 1799–1962
hierarchical_section_title: Metrication in the United Kingdom / History / 1799–1962
caption_attribution_description: English: Joules Heat Apparatus 1845, Science Museum, London. 02-Jan-06. Français&#160;: Dispositif expérimental montrant l'équivalence entre chaleur et travail (1845).
context_page_description: Metrication in the United Kingdom, the process of introducing the metric system of measurement in place of imperial units, has made steady progress since the mid–20th century but today remains equivocal and varies by context. Most of government, industry and commerce use metric units, but imperial units are officially used to specify journey distances, vehicle speeds and the sizes of returnable milk containers, beer and cider glasses. Imperial units are also often used to describe body measurements and vehicle fuel economy. In schools metric units are taught and used as the norm. Imperial units that remain in common usage in the UK are also taught.
  Adopting the metric system was discussed in Parliament as early as 1818 and some industries and even some government agencies had metricated, or were in the process of metricating by the mid-1960s. A formal government policy to support metrication was agreed by 1965. This policy, initiated in response to requests from industry, was to support voluntary metrication, with costs picked up where they fell. In 1969 the government created the Metrication Board as a quango to promote and coordinate metrication.
context_section_description: In 1799, the French created, and started to use, a new system with the metre and the kilogram as the units of length and mass. As use of this new system, originally called the "Decimal System", spread through Europe, there were some calls in the United Kingdom for decimalisation. The issue of decimalisation of measurement was intertwined in the United Kingdom with decimalisation of currency. The idea was first discussed by a Royal Commission that reported in 1818, and again in Parliament by Sir John Wrottesley in 1824. Another Royal Commission was set up 1838 by Chancellor of the Exchequer Thomas Spring Rice and it reported in 1841 that decimal coinage was required first. A third commission in 1853 advocated decimal coinage in the form £1 : 10 florins : 100 cents: 1000 mils. The first florins (one tenth of a pound sterling) were struck in 1849 as silver coins weighing 11.3 grams (defined as ​⁴⁄₁₁ troy ounce) and having a diameter of 28 millimetres (1.1 inches).
  An early supporter of the Decimal Association was the mathematician Augustus de Morgan whose articles supporting the metric system had been published in the Penny Cyclopeadia (1833) and The Companion to the Almanac (1841). A few days later Wrottesley met with Gladstone, then Chancellor of the Exchequer, but was unable to win him over to the idea. The inherent problems associated with handling multiple currencies and systems of units encountered in the  Great Exhibition of 1851 triggered calls for a standardisation of units across Europe with the metric system being suggested as the natural choice. In 1854, de Morgan was influential in setting up the "Decimal Association" to lobby for decimalisation of both measurement and coinage. In 1862, the Select committee on Weights and Measures favoured the introduction of decimalisation to accompany the introduction of metric weights and measures. A further Royal Commission "on the question of the introduction of metric system of weights and measures" also reported in 1869.
  In 1863, a bill which would have mandated the use of the metric system throughout the British Empire, and which had passed its first and second readings in the House of Commons, was rejected at its Commons Committee stage as impractical, and so did not pass into law. The following year, after pressure from the astronomers George Airy and Sir John Herschel, the bill was watered down to merely legalise the use of the metric system in contracts. It was presented and passed as a Private Member's Bill. Ambiguous wording in the 1864 Act meant that traders who possessed metric weights and measures were still liable to arrest under the Weights and Measures Act 1835 5° & 6° William IV. Cap. 63.
  While the politicians were discussing whether or not to adopt the metric system, British scientists were in the forefront in developing the system. In 1845, a paper by James Prescott Joule proved the equivalence of mechanical and thermal energy, a concept that is vital to the metric system – in SI, power is measured in watts and energy in joules regardless of whether it is mechanical, electrical or thermal.
  In 1861, a committee of the British Association for Advancement of Science (BAAS) including William Thomson (later Lord Kelvin), James Clerk Maxwell and Joule among its members was tasked with investigating the "Standards of Electrical Resistance". In their first report (1862), they laid the ground rules for their work – the metric system was to be used and measures of electrical energy must have the same units as measures of mechanical energy. 
  In the second report (1863), they introduced the concept of a coherent system of units whereby units of length, mass and time were identified as "fundamental units" (now known as base units). 
  All other units of measure could be derived (hence derived units) from these base units.
  In 1873, another committee of the BAAS that also counted Maxwell and Thomson among its members and was tasked with "the Selection and Nomenclature of Dynamical and Electrical Units". They recommended the CGS (centimetre-gram-second) system of units. Th
caption: Joule's Heat Apparatus, 1845
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