Kilogram Explained

kilogram
Standard:SI
Quantity:mass
Symbol:kg
Units1:Avoirdupois
Units2:British Gravitational
Inunits2:≈ slugs
Units3:CGS units
Inunits3:1000 grams
Units4:Atomic mass units
Inunits4: Da

The kilogram (also kilogramme) is the base unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially.[1] It means 'one thousand grams'.

The kilogram is a SI base unit, defined in terms of two other base units, the second and the metre and the Planck constant, a SI defining constant. A properly equipped metrology laboratory can calibrate a mass measurement instrument such as a Kibble balance as a primary standard for the kilogram mass.[2]

The kilogram was originally defined in 1795 during the French Revolution as the mass of one litre of water. The current definition of a kilogram agrees with this original definition to within 30 parts per million. In 1799, the platinum Kilogramme des Archives replaced it as the standard of mass. In 1889, a cylinder of platinum-iridium, the International Prototype of the Kilogram (IPK), became the standard of the unit of mass for the metric system and remained so for 130 years, before the current standard was adopted in 2019.

Definition

The kilogram is defined in terms of three defining constants:

The formal definition according to the General Conference on Weights and Measures (CGPM) is:Defined in term of those units, the kg is formulated as:[3]

kg = = ≈ .

This definition is generally consistent with previous definitions: the mass remains within 30 ppm of the mass of one litre of water.[4]

Timeline of previous definitions

Name and terminology

The kilogram is the only base SI unit with an SI prefix (kilo) as part of its name. The word kilogramme or kilogram is derived from the French French: kilogramme, which itself was a learned coinage, prefixing the Greek stem of Greek, Ancient (to 1453);: χίλιοι "a thousand" to Latin: gramma, a Late Latin term for "a small weight", itself from Greek Greek, Ancient (to 1453);: γράμμα.[9] The word French: kilogramme was written into French law in 1795, in the Decree of 18 Germinal,[10] which revised the provisional system of units introduced by the French National Convention two years earlier, where the French: gravet had been defined as weight (French: poids) of a cubic centimetre of water, equal to 1/1000 of a French: [[Grave (unit)|grave]].[11] In the decree of 1795, the term French: gramme thus replaced French: gravet, and French: kilogramme replaced French: grave.[7]

The French spelling was adopted in Great Britain when the word was used for the first time in English in 1795,[12] [13] with the spelling kilogram being adopted in the United States. In the United Kingdom both spellings are used, with "kilogram" having become by far the more common.[14] UK law regulating the units to be used when trading by weight or measure does not prevent the use of either spelling.[15]

In the 19th century the French word French: kilo, a shortening of French: kilogramme, was imported into the English language where it has been used to mean both kilogram[16] and kilometre.[17] While kilo as an alternative is acceptable, to The Economist for example,[18] the Canadian government's Termium Plus system states that "SI (International System of Units) usage, followed in scientific and technical writing" does not allow its usage and it is described as "a common informal name" on Russ Rowlett's Dictionary of Units of Measurement.[19] [20] When the United States Congress gave the metric system legal status in 1866, it permitted the use of the word kilo as an alternative to the word kilogram,[21] but in 1990 revoked the status of the word kilo.[22]

The SI system was introduced in 1960 and in 1970 the BIPM started publishing the SI Brochure, which contains all relevant decisions and recommendations by the CGPM concerning units. The SI Brochure states that "It is not permissible to use abbreviations for unit symbols or unit names ...".[23]

For use with east Asian character sets, the SI symbol is encoded as a single Unicode character, in the CJK Compatibility block.

Redefinition based on fundamental constants

See main article: 2019 redefinition of the SI base units.

The replacement of the International Prototype of the Kilogram (IPK) as the primary standard was motivated by evidence accumulated over a long period of time that the mass of the IPK and its replicas had been changing; the IPK had diverged from its replicas by approximately 50 micrograms since their manufacture late in the 19th century. This led to several competing efforts to develop measurement technology precise enough to warrant replacing the kilogram artefact with a definition based directly on physical fundamental constants.[24]

The International Committee for Weights and Measures (CIPM) approved a redefinition of the SI base units in November 2018 that defines the kilogram by defining the Planck constant to be exactly, effectively defining the kilogram in terms of the second and the metre. The new definition took effect on May 20, 2019.[24] [25]

Prior to the redefinition, the kilogram and several other SI units based on the kilogram were defined by a man-made metal artifact: the Kilogramme des Archives from 1799 to 1889, and the IPK from 1889 to 2019.[24]

In 1960, the metre, previously similarly having been defined with reference to a single platinum-iridium bar with two marks on it, was redefined in terms of an invariant physical constant (the wavelength of a particular emission of light emitted by krypton, and later the speed of light) so that the standard can be independently reproduced in different laboratories by following a written specification.

At the 94th Meeting of the CIPM in 2005, it was recommended that the same be done with the kilogram.[26]

In October 2010, the CIPM voted to submit a resolution for consideration at the General Conference on Weights and Measures (CGPM), to "take note of an intention" that the kilogram be defined in terms of the Planck constant, (which has dimensions of energy times time, thus mass × length / time) together with other physical constants.[27] [28] This resolution was accepted by the 24th conference of the CGPM[29] in October 2011 and further discussed at the 25th conference in 2014.[30] [31] Although the Committee recognised that significant progress had been made, they concluded that the data did not yet appear sufficiently robust to adopt the revised definition, and that work should continue to enable the adoption at the 26th meeting, scheduled for 2018. Such a definition would theoretically permit any apparatus that was capable of delineating the kilogram in terms of the Planck constant to be used as long as it possessed sufficient precision, accuracy and stability. The Kibble balance is one way to do this.[32]

As part of this project, a variety of very different technologies and approaches were considered and explored over many years. Some of these approaches were based on equipment and procedures that would enable the reproducible production of new, kilogram-mass prototypes on demand (albeit with extraordinary effort) using measurement techniques and material properties that are ultimately based on, or traceable to, physical constants. Others were based on devices that measured either the acceleration or weight of hand-tuned kilogram test masses and which expressed their magnitudes in electrical terms via special components that permit traceability to physical constants. All approaches depend on converting a weight measurement to a mass and therefore require precise measurement of the strength of gravity in laboratories (gravimetry). All approaches would have precisely fixed one or more constants of nature at a defined value.

SI multiples

See main article: Orders of magnitude (mass).

Because an SI unit may not have multiple prefixes (see SI prefix), prefixes are added to gram, rather than the base unit kilogram, which already has a prefix as part of its name.[33] For instance, one-millionth of a kilogram is 1mg (one milligram), not 1μkg (one microkilogram).

Practical issues with SI weight names

See also

Notes

  1. https://www.merriam-webster.com/dictionary/kilo Merriam-Mebster definition of Kilo
  2. Web site: July 7, 2021 . Mise en pratique for the definition of the kilogram in the SI . February 18, 2022 . BIPM.org.
  3. https://www.bipm.org/en/publications/si-brochure/ SI Brochure: The International System of Units (SI)
  4. The density of water is at . See Book: Franks, Felix . The Physics and Physical Chemistry of Water . 2012 . Springer . 978-1-4684-8334-5.
  5. Book: Annales de chimie ou Recueil de mémoires concernant la chimie et les arts qui en dépendent . 1792. Paris . Chez Joseph de Boffe . 277 . 15–16. Guyton. Lavoisier. Monge. Berthollet. etal. Louis-Bernard Guyton de Morveau. Antoine Lavoisier. Gaspard Monge. Claude Louis Berthollet.
  6. French: Gramme, le poids absolu d'un volume d'eau pure égal au cube de la centième partie du mètre, et à la température de la glace fondante
  7. Book: Zupko, Ronald Edward. Ronald Edward Zupko. 1990 . Revolution in Measurement: Western European Weights and Measures Since the Age of Science . Philadelphia . American Philosophical Society . 978-0-87169-186-6.
  8. Encyclopedia: Treaty of the Metre. Encyclopædia Britannica. 18 July 2023. 2023.
  9. Book: The Concise Oxford Dictionary. 1964. HW. Fowlers. FG. Fowler. The Clarendon Press. Oxford. Greek Greek, Ancient (to 1453);: γράμμα (as it were Greek, Ancient (to 1453);: [[:wikt:γράφω|γράφ]]-[[:wikt:-μα|μα]], Doric Greek, Ancient (to 1453);: γράθμα) means "something written, a letter", but it came to be used as a unit of weight, apparently equal to of an ounce (of a Latin: [[Pound (mass)#Roman libra|libra]], which would correspond to about 1.14 grams in modern units), at some time during Late Antiquity. French French: gramme was adopted from Latin Latin: gramma, itself quite obscure, but found in the Latin: Carmen de ponderibus et mensuris (8.25) attributed by Remmius Palaemon (fl. 1st century), where it is the weight of two Latin: [[obolus|oboli]] (Charlton T. Lewis, Charles Short, A Latin Dictionary s.v. "gramma", 1879).Henry George Liddell. Robert Scott. A Greek-English Lexicon (revised and augmented edition, Oxford, 1940) s.v. γράμμα, citing the 10th-century work Geoponica and a 4th-century papyrus edited in L. Mitteis, Griechische Urkunden der Papyrussammlung zu Leipzig, vol. i (1906), 62 ii 27.
  10. Web site: Décret relatif aux poids et aux mesures du 18 germinal an 3 (7 avril 1795). fr. Decree of 18 Germinal, year III (April 7, 1795) regarding weights and measures. Grandes lois de la République. Digithèque de matériaux juridiques et politiques, Université de Perpignan. November 3, 2011.
  11. French: Convention nationale, décret du 1<sup>er</sup> août 1793, ed. Duvergier, ''Collection complète des lois, décrets, ordonnances, règlemens avis du Conseil d'état, publiée sur les éditions officielles du Louvre''|italic=unset, vol. 6 (2nd ed. 1834), p. 70.The metre (French: mètre) on which this definition depends was itself defined as the ten-millionth part of a quarter of Earth's meridian, given in traditional units as 3 French: [[foot (unit)|pieds]], 11.44 French: lignes (a French: ligne being the 12th part of a French: pouce (inch), or the 144th part of a French: pied.
  12. Paris, during the year 1795. Peltier, Jean-Gabriel . Monthly Review . 1795 . 17. 556. August 2, 2018. Contemporaneous English translation of the French decree of 1795
  13. Web site: Kilogram. Oxford English Dictionary. Oxford University Press. November 3, 2011.
  14. Web site: Kilogram . Oxford Dictionaries . November 3, 2011 . dead . https://archive.today/20130131014115/http://english.oxforddictionaries.com/definition/kilogram . January 31, 2013 . mdy-all.
  15. Web site: Spelling of "gram", etc . . . October 30, 1985 . November 6, 2011.
  16. Encyclopedia: 1989 . 2nd . kilo (n1) . . Oxford University Press . Oxford . November 8, 2011.
  17. Encyclopedia: 1989 . 2nd . kilo (n2) . . Oxford University Press . Oxford . November 8, 2011.
  18. News: Style Guide . . January 7, 2002 . https://web.archive.org/web/20170701053545/http://www.frzee.com/Education/The%20Economist%20Style%20Guide.pdf . July 1, 2017 . dead . November 8, 2011.
  19. Web site: kilogram, kg, kilo . Termium Plus . Government of Canada . October 8, 2009 . May 29, 2019 .
  20. Web site: kilo . How Many? . November 6, 2011 . dead . https://web.archive.org/web/20111116205434/http://www.unc.edu/~rowlett/units/dictK.html . November 16, 2011.
  21. Web site: H.R. 596, An Act to authorize the use of the metric system of weights and measures . 29th Congress of the United States, Session 1 . May 13, 1866 . dead . https://web.archive.org/web/20150705015307/http://lamar.colostate.edu/~hillger/laws/metric-act-bill.html . July 5, 2015.
  22. . 63 . 144 . July 28, 1998 . 40340 . Metric System of Measurement:Interpretation of the International System of Units for the United States; Notice . Obsolete Units As stated in the 1990 Federal Register notice, ... . November 10, 2011 . dead . https://web.archive.org/web/20111015081850/http://physics.nist.gov/cuu/pdf/SIFedReg.pdf . October 15, 2011 . mdy-all.
  23. The French text (which is the authoritative text) states "French: Il n'est pas autorisé d'utiliser des abréviations pour les symboles et noms d'unités ..."
  24. News: Resnick . Brian . The new kilogram just debuted. It's a massive achievement. . May 23, 2019 . vox.com . May 20, 2019.
  25. News: Kilogram gets a new definition . Pallab Ghosh . November 16, 2018 . BBC News . November 16, 2018.
  26. Recommendation 1: Preparative steps towards new definitions of the kilogram, the ampere, the kelvin and the mole in terms of fundamental constants . 94th meeting of the International Committee for Weights and Measures . October 2005 . 233 . February 7, 2018 . live . https://web.archive.org/web/20070630011658/https://www.bipm.org/cc/CIPM/Allowed/94/CIPM-Recom1CI-2005-EN.pdf . June 30, 2007.
  27. NIST Backs Proposal for a Revamped System of Measurement Units . NIST . October 26, 2010 . Nist.gov . April 3, 2011.
  28. Web site: Draft Chapter 2 for SI Brochure, following redefinitions of the base units . Ian Mills . CCU . September 29, 2010 . January 1, 2011.
  29. Resolution 1 – On the possible future revision of the International System of Units, the SI . 24th meeting of the General Conference on Weights and Measures . Sèvres, France . October 17–21, 2011 . October 25, 2011.
  30. Web site: BIPM – Resolution 1 of the 25th CGPM. www.bipm.org. March 27, 2017.
  31. General Conference on Weights and Measures approves possible changes to the International System of Units, including redefinition of the kilogram. . . Sèvres, France . October 23, 2011 . October 25, 2011.
  32. 10.1088/0026-1394/53/5/A46 . The watt or Kibble balance: A technique for implementing the new SI definition of the unit of mass . Metrologia . 53 . 5 . A46–A74 . 2016 . Robinson . Ian A. . Schlamminger . Stephan . 35023879 . 8752041 . 2016Metro..53A..46R . free .
  33. BIPM: SI Brochure: Section 3.2, The kilogram
  34. Web site: Prescribing Information for Liquid Medicines . Scottish Palliative Care Guidelines . June 15, 2015 . https://web.archive.org/web/20180710152658/http://www.palliativecareguidelines.scot.nhs.uk/guidelines/about-the-guidelines/pharmacological-considerations/prescribing-information-for-liquid-medicines.aspx . July 10, 2018 . dead .
  35. Web site: New Joint Commission "Do Not Use" List: Abbreviations, Acronyms, and Symbols . American Academy of Physical Medicine and Rehabilitation . 19 February 2024 . https://web.archive.org/web/20150915012112/http://www.aapmr.org/practice/guidelines/Pages/New-Joint-Commission-symbols.aspx . 15 September 2015.
  36. Web site: Prescription writing . . 19 February 2024.
  37. Tom Stobart, The Cook's Encyclopedia, 1981, p. 525
  38. J.J. Kinder, V.M. Savini, Using Italian: A Guide to Contemporary Usage, 2004,, p. 231
  39. Giacomo Devoto, Gian Carlo Oli, Nuovo vocabolario illustrato della lingua italiana, 1987, s.v. 'ètto': "frequentissima nell'uso comune: un e. di caffè, un e. di mortadella; formaggio a 2000 lire l'etto"
  40. U.S. National Bureau of Standards, The International Metric System of Weights and Measures, "Official Abbreviations of International Metric Units", 1932, p. 13
  41. Web site: Jestřebická hovězí šunka 10 dkg Rancherské speciality . eshop.rancherskespeciality.cz . cs. June 16, 2020. https://web.archive.org/web/20200616032253/https://eshop.rancherskespeciality.cz/Jestrebicka-hovezi-sunka-10-dkg-d189.htm. June 16, 2020.
  42. Web site: Sedliacka šunka 1 dkg Gazdovský dvor – Farma Busov Gaboltov . Sedliacka šunka 1 dkg . sk. June 16, 2020. https://web.archive.org/web/20200616033111/http://farmabusoveshop.sk/sedliacka-sunka-1-dkg. June 16, 2020.
  43. Web site: sýr bazalkový – Farmářské Trhy . www.e-farmarsketrhy.cz . cs. June 16, 2020. https://web.archive.org/web/20200616033522/http://www.e-farmarsketrhy.cz/syry-z-kravskeho-mleka/syr-bazalkovy. June 16, 2020.
  44. Web site: English Menu – Cafe Mediterran . en. June 16, 2020. https://web.archive.org/web/20200616034445/http://www.mediterrangrill.hu/english-menu/. June 16, 2020. Beef steak 20 dkg; Beef steak 40 dkg;Thick crust 35 dkg.
  45. Web site: Termékek – Csíz Sajtműhely . hu. June 16, 2020. https://web.archive.org/web/20200616035724/https://csizsajtmuhely.hu/sajtrendeles/. June 16, 2020.
  46. Non-SI units that are accepted for use with the SI, SI Brochure: Section 4 (Table 8), BIPM

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