International yard and pound

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The international yard and pound are two units of measurement that were the subject of an agreement among representatives of six nations signed on 1 July 1959; the United States, United Kingdom, Canada, Australia, New Zealand, and South Africa. The agreement defined the yard as exactly 0.9144 meters and the (avoirdupois) pound as exactly 0.45359237 kilograms.[1]


In October 1834, the United Kingdom Houses of Parliament were destroyed in a fire. Among the items lost were the objects that defined the imperial standards of length and mass. New prototypes were subsequently created to replace the items lost in the fire, among them a new "yardstick" ruler in 1855, and with it a new formal definition of the yard. Two copies of the ruler were subsequently presented to the United States, which in turn adopted the measure for the United States national standard yard.

In 1866, the U.S. Congress passed a law that allowed, but did not require, the use of the metric system in trade and commerce. Included in the law was a table of conversion factors between the customary (i.e. British-derived) and metric units, among them a definition of the meter in terms of the yard, and the kilogram in terms of the pound. In 1893, the Mendenhall Order changed the fundamental standards of length and mass of the United States from the customary standards based on those of England to metric standards.[2][3] There were two factors that influenced the order: for one, the imperial standard yard of 1855 had been found to be unstable and shortening by measurable amounts. Secondly, the United States was a co-signee of the Treaty of the Metre of 1875 and had received two meter prototypes on which to base a new fundamental standard.

In the United Kingdom, a similar situation developed with the Weights and Measures Act of 1897 legalizing the metric system,[4] and Order in Council 411 (1898) defining the meter and kilogram in terms of the yard and pound.[5] As a practical matter the British definitions were reversed, resulting in a de facto definition of the imperial yard as 36/39.370113 meter.[6]

In the 1890s, Albert Michelson began conducting experiments in interferometry that led in 1903 to demonstrating the feasibility of using light waves as units of linear measurement. In 1908, two teams of researchers, one led by Michelson, defined the length of the international prototype meter in terms of light waves. In 1927, the International Bureau of Weights and Measures provisionally adopted the 1908 light-wave definition of the meter as a supplemental standard.[7]

In 1930, the British Standards Institution adopted an inch of exactly 25.4 millimetres (mm), based on the 1927 light-wave definition of the meter. The American Standards Association followed suit in 1933. By 1935, industry in 16 countries had adopted the "industrial inch" as it came to be known.[8][9] In 1946, the British Commonwealth Scientific Conference recommended that members of the British Commonwealth adopt the inch as exactly 25.4 mm, and the 36-inch yard as exactly 0.9144 meters.[10][11] The British Commonwealth Scientific Conference's recommendations were accepted by the Canadian Standards Association in 1951.[12]

In October 1958, the International Committee on Weights and Measures made a recommendation that the meter be defined in atomic terms (specifically in terms of the orange line of krypton-86). To secure identical values for the yard and pound in precise measurements, representatives of six English-speaking nations—Australia, Canada, New Zealand, South Africa, United States and United Kingdom—agreed to adopt a common 'international yard and international pound'. According to that agreement, the international yard equals 0.9144 meters and the international pound equals 0.45359237 kilograms.[1] The international yard was about two millionths of a meter longer than the imperial yard, while the international pound was about six ten-millionths of a kilogram lighter than the imperial pound.[13]

The metric-based international yard and international pound were adopted by the United States National Bureau of Standards effective 1 July 1959.[14][15] In Australia, the international yard and pound were instituted through Statutory Rule No. 142 of 1961, effective 1 January 1964.[16] The UK adopted the international yard and pound for all purposes through the Weights and Measures Act of 1963, effective 1 January 1964.[17]

See also[edit]


  1. ^ a b United States. National Bureau of Standards (1959). Research Highlights of the National Bureau of Standards. U.S. Department of Commerce, National Bureau of Standards. p. 13. Retrieved 31 July 2019.
  2. ^ National Bureau of Standards, Refinement of values for the yard and pound
  3. ^ Bewoor, Arand K.; Kulkarni, Vinay A. (2009). Metrology & Measurement. Tata McGraw-Hill Education. p. 18. ISBN 978-0-07-014000-4. Retrieved 16 September 2012.
  4. ^ John Mews, ed. (1897). "Statutes of the Realm - 60-61 Victoria". The Law journal reports. Vol. 66. London: The Law Journal Reports. p. 109. Retrieved 16 September 2012.
  5. ^ Great Britain; Pulling, Alexander; Great Britain. Statute Law Committee (1904). The statutory rules and orders revised: being the statutory rules and orders (other than those of a local, personal, or temporary character) in force on December 31, 1903 ... Vol. 13 (2nd ed.). section 4 - Weights and Measures: HMSO. pp. 4:25–27. Retrieved 17 September 2012.{{cite book}}: CS1 maint: location (link)
  6. ^ Connor, R D (1987). The Weights and Measures of England. H.M. Stationery Office. ISBN 978-0-11-290435-9. Retrieved 17 September 2012.
  7. ^ Estermann, Immanuel (1959). Classical Methods. Academic Press. p. 27. ISBN 978-0-12-475901-5. Retrieved 16 September 2012.
  8. ^ National Conference on Weights and Measures; United States. Bureau of Standards; National Institute of Standards and Technology (U.S.) (1936). Report of the ... National Conference on Weights and Measures. U.S. Department of Commerce, Bureau of Standards. p. 4. Retrieved 2 August 2012.
  9. ^ Wandmacher, Cornelius; Johnson, Arnold Ivan (1995). Metric Units in Engineering--going SI: How to Use the International Systems of Measurement Units (SI) to Solve Standard Engineering Problems. ASCE Publications. p. 265. ISBN 978-0-7844-0070-8. Retrieved 2 August 2012.
  10. ^ Report of the British Commonwealth Scientific Conference. Official Conference, London, 1946. Cmd. 6970. H.M. Stationery Office, 1946
  11. ^ implicitly and logically also defining a 12-inch foot as 30.48 centimetres.
  12. ^ Canadian Journal of Physics, 1959, 37(1): 84, 10.1139/p59-014
  13. ^ "Synchronize Yardsticks!". Popular Mechanics. Hearst Magazines. March 1959. p. 248.
  14. ^ Lewis Van Hagen Judson; United States. National Bureau of Standards (1976). Weights and measures standards of the United States: a brief history. Dept. of Commerce, National Bureau of Standards : for sale by the Supt. of Docs., U.S. Govt. Print. Off. pp. 30–1. Retrieved 16 September 2012.
  15. ^ National Conference on Weights and Measures; United States. Bureau of Standards; National Institute of Standards and Technology (U.S.) (1957). Report of the ... National Conference on Weights and Measures. U.S. Department of Commerce, Bureau of Standards. pp. 45–6. Retrieved 2 August 2012.
  16. ^ Australian Government ComLaw Weights and Measures (National Standards) Regulations - C2004L00578
  17. ^ Thoburn v Sunderland City Council [2002] EWHC 195 (Admin) (18 February 2002)