Inch#International inch

The English word "inch" ({{langx|ang|ynce}}) was an early borrowing from Latin {{lang|la|uncia}} ("one-twelfth; Roman inch; Roman ounce").{{citation |contribution=inch, n.¹ |title=Oxford English Dictionary |location=Oxford |publisher=Oxford University Press }}. The vowel change from Latin {{IPA|/u/}} to Old English {{IPA|/y/}} (which became Modern English {{IPA|/ɪ/}}) is known as umlaut.{{citation needed|date=October 2022}} The consonant change from the Latin {{IPA|/k/}} (spelled c) to English {{IPA|/tʃ/}} is palatalisation. Both were features of Old English phonology; see {{section link|Phonological history of Old English|Palatalization}} and {{section link|Germanic umlaut|I-mutation in Old English}} for more information.

"Inch" is cognate with "ounce" ({{langx|ang|ynse}}), whose separate pronunciation and spelling reflect its reborrowing in Middle English from Anglo-Norman unce and ounce.{{citation |contribution=ounce, n.¹ |title=Oxford English Dictionary |location=Oxford |publisher=Oxford University Press }}.

In many other European languages, the word for "inch" is the same as or derived from the word for "thumb", as a man's thumb is about an inch wide (and this was even sometimes used to define the inch{{Cite web|url=https://www.britannica.com/science/inch|title=Inch {{!}} unit of measurement|website=Encyclopedia Britannica|language=en|access-date=28 March 2019}}). In the Dutch language a term for inch is engelse duim (english thumb).{{cite web |url=https://onzetaal.nl/taalloket/duim-lengtemaat |title=duim - lengtemaat |publisher=Genootschap Onze Taal|access-date=22 October 2022}}{{cite web |url=https://www.omrekenen.nl/duim/ |title=duim |date=24 May 2020 |access-date=22 October 2022}} Examples include {{langx|ca|polzada}} ("inch") and {{lang|ca|polze}} ("thumb"); {{langx|cs|palec}} ("thumb"); Danish and {{langx|no|tomme}} ("inch") {{lang|no|tommel}} ("thumb"); {{langx|nl|duim}} (whence {{langx|af|duim}} and {{langx|ru|дюйм}}); {{langx|fr|pouce}}; {{lang-ka|დუიმი}}, {{langx|hu|hüvelyk}}; {{langx|it|pollice}}; {{langx|pt|polegada}} ("inch") and {{lang|pt|polegar}} ("thumb"); ("duim"); {{langx|sk|palec}} ("thumb"); {{langx|es|pulgada}} ("inch") and {{lang|es|pulgar}} ("thumb"); and {{langx|sv|tum}} ("inch") and tumme ("thumb").

The inch is a commonly used customary unit of length in the United States,{{cite web |url=http://corpus.byu.edu/coca/ |title=Corpus of Contemporary American English |website=Brigham Young University |location=US |access-date=5 December 2011}} lists 24,302 instances of inch(es) compared to 1548 instances of centimeter(s) and 1343 instances of millimeter(s). Canada,{{cite web |url=http://laws-lois.justice.gc.ca/PDF/W-6.pdf |title=Weights and Measures Act |page=37 |via=Justice Laws Website |location=Canada |year=1985 |access-date=11 January 2018}}{{cite web |url=http://laws-lois.justice.gc.ca/eng/acts/W-6/page-2.html#h-4/ |title=Weights and Measures Act |page=2 |via=Justice Laws Website |location=Canada |date=1 August 2014 |access-date=18 December 2014}} Canadian units (5) The Canadian units of measurement are as set out and defined in Schedule II, and the symbols and abbreviations therefore are as added pursuant to subparagraph 6(1)(b)(ii). and the United Kingdom. For the United Kingdom, guidance on public sector use states that, since 1 October 1995, without time limit, the inch (along with the foot) is to be used as a primary unit for road signs and related measurements of distance (with the possible exception of clearance heights and widths){{cite web |url=http://www.legislation.gov.uk/uksi/2002/3113/schedule/2/made |title=The Traffic Signs Regulations and General Directions 2002 - No. 3113 - Schedule 2 - Regulatory Signs |publisher=The National Archives |location=UK |year=2002 |access-date=25 April 2013}} and may continue to be used as a secondary or supplementary indication following a metric measurement for other purposes.{{cite web |url=http://www.bis.gov.uk/assets/bispartners/nmo/docs/legislation/legislation/units-of-measurement/gnotes-for-public-sector-on-use-of-metric.pdf |archive-url=https://web.archive.org/web/20110704232045/http://www.bis.gov.uk/assets/bispartners/nmo/docs/legislation/legislation/units-of-measurement/gnotes-for-public-sector-on-use-of-metric.pdf |url-status=dead |archive-date=4 July 2011 |title=Guidance Note on the use of Metric Units of Measurement by the Public Sector |publisher=Department for Business Innovation and Skills |location=UK |year=2007 |access-date=12 December 2014}}

Inches are used for display screens (e.g. televisions and computer monitors) worldwide. It is the official Japanese standard for electronic parts, especially display screens, and is the industry standard throughout continental Europe for display screens (Germany being one of few countries to supplement it with centimetres in most stores{{Cite web|url=https://www.otto.de/technik/fernseher/|title=Fernseher|publisher=Otto GmbH|language=de|access-date=28 December 2023}}).

Inches are commonly used to specify the diameter of vehicle wheel rims, and the corresponding inner diameter of tyres in tyre codes.{{Cite web|url=https://www.michelin.co.uk/auto/advice/tyre-basics/tyre-markings-explained|title=Tyre Sizing|access-date=14 May 2025}}

The international standard symbol for inch is in (see ISO 31-1, Annex A) but traditionally the inch is denoted by a double prime, which is often approximated by a double quote symbol, and the foot by a prime, which is often approximated by an apostrophe. For example; {{nowrap|three feet, two inches}} can be written as 3{{prime}} 2{{pprime}}. (This is akin to how the first and second "cuts" of the hour are likewise indicated by prime and double prime symbols, and also the first and second cuts of the degree.)

Subdivisions of an inch are typically written using dyadic fractions with odd number numerators; for example, {{nowrap|two and three-eighths of an inch}} would be written as {{sfrac|2|3|8}}{{pprime}} and not as 2.375{{pprime}} nor as {{sfrac|2|6|16}}{{pprime}}. However, for engineering purposes fractions are commonly given to three or four places of decimals and have been for many years.{{cite book|last1=Flatchet|first1=E|last2=Petiet|first2=J|title=The student's guide to the locomotive engine|url=https://archive.org/details/studentsguideto00ptgoog|date=1849|publisher=John Williams and Co|page=xi|quote=One Metre is equal to ... 30.371 inches"}}{{cite book|last=Parkinson|first=A C |title=Intermediate Engineering Drawing|date=1967|edition=sixth|page=11|quote=The basic major dia is actually 1.309 in.}}

{{calculator|id=in|type=number|size=4|default=1}} international inch is equal to:

{{div col|colwidth=30em}}

• {{calculator|id=cm|type=plain|default=2.54|formula=in*2.54|decimals=1|NaN-text=0}} centimeters (1 inch is exactly 2.54 cm)
• {{calculator|id=mm|type=plain|default=25.4|formula=in*25.4|decimals=1|NaN-text=0}} millimetres (1 inch is exactly 25.4 mm)
• {{sfrac|{{calculator|id=numeratorfeet|type=plain|default=1|formula=in|NaN-text=0}}|12}} or {{calculator|id=feet|type=plain|default=0.08333|formula=in/12|NaN-text=0}} feet (approximately)
• {{sfrac|{{calculator|id=numeratoryards|type=plain|default=1|formula=in|NaN-text=0}}|36}} or {{calculator|id=yard|type=plain|default=0.02777|formula=in/36|NaN-text=0}} yards (approximately)
• {{calculator|id=tenths|type=plain|default=10000|formula=in*10000|NaN-text=0}} 'tenths'{{efn|A tenth of a thou, used in machining.}}
• {{calculator|id=thou|type=plain|default=1000|formula=in*1000|NaN-text=0}} thou{{efn|Used in machining and papermaking.}} or mil{{efn|Formerly used in American English but now often avoided to prevent confusion with millimetres.}}
• {{calculator|id=points|type=plain|default=100|formula=in*100|NaN-text=0}} points{{efn|Used by the Australian Bureau of Meteorology for measuring rainfall until 1973{{cite web |url=http://www.bom.gov.au/climate/cdo/about/definitionsrain.shtml |title=Climate Data Online – definition of rainfall statistics |publisher=Bureau of Meteorology |location=Australia |access-date=10 June 2012}}}} or gries{{efn|name=locke|Part of John Locke's proposal for decimalization of English measures{{citation |last=Locke |first=John |author-link=John Locke |display-authors=0 |contribution=Of Human Understanding |page=[https://books.google.com/books?id=3n8PAAAAQAAJ&pg=PA293 293] |title=The Works of John Locke Esq., Vol. I |location=London |publisher=John Churchill |date=1714 |url=https://books.google.com/books?id=3n8PAAAAQAAJ }}.}}
• {{calculator|id=pointsTypography|type=plain|default=72|formula=in*72|NaN-text=0}} PostScript points{{efn|The typographic point was originally {{sfrac|1|9}} of the height of a (capital) letter (cap height) but later acquired a number of different absolute definitions; see Point (typography) § History for details.}}
• {{calculator|id=line10|type=plain|default=10|formula=in*10|NaN-text=0}},{{efn|Used in gunmaking.}} {{calculator|id=line12|type=plain|default=12|formula=in*12|NaN-text=0}},{{efn|Used in botany.}} or {{calculator|id=line40|type=plain|default=40|formula=in*40|NaN-text=0}}{{efn|Used in button manufacturing.}} lines
• {{calculator|id=pica|type=plain|default=6|formula=in*6|NaN-text=0}} computer picas{{efn|Used in typography.}}
• {{calculator|id=barleycorn|type=plain|default=3|formula=in*3|NaN-text=0}} barleycorns{{efn|Used in American and British shoe sizes.}}
• {{calculator|id=ussurveyin|type=plain|default=0.999998|formula=in*0.999998|NaN-text=0}} US survey inches
• {{sfrac|{{calculator|id=numeratorPalm|type=plain|default=1|formula=in|NaN-text=0}}|3}} or {{calculator|id=palms|type=plain|default=0.333|formula=in/3|NaN-text=0}} palms (approximately)
• {{sfrac|{{calculator|id=numeratorhand|type=plain|default=1|formula=in|NaN-text=0}}|4}} or {{calculator|id=hand|type=plain|default=0.25|formula=in/4|NaN-text=0}} hands{{efn|Used in measuring the height of horses.}}

{{Div col end}}

File:Inch converter.jpg

The earliest known reference to the inch in England is from the Laws of Æthelberht dating to the early 7th century, surviving in a single manuscript, the Textus Roffensis from 1120.{{cite book |last1=Goetz |first1=Hans-Werner |last2=Jarnut |first2=Jörg |last3=Pohl |first3=Walter |author-link3=Walter Pohl |title=Regna and Gentes: The Relationship Between Late Antique and Early Medieval Peoples and Kingdoms in the Transformation of the Roman World |url=https://books.google.com/books?id=RovRlJkrncEC&pg=PA33 |year=2003 |publisher=BRILL |isbn=978-90-04-12524-7 |page=33}} Paragraph LXVII sets out the fine for wounds of various depths: one inch, one shilling; two inches, two shillings, etc.{{efn|{{langx|ang|Gif man þeoh þurhstingð, stice ghwilve vi scillingas. Gife ofer ynce, scilling. æt twam yncum, twegen. ofer þry, iii scill.}} Translation (taken from {{harvnb|Attenborough|1922|p=13}}): If a thigh is pierced right through, 6 shillings compensation shall be paid for each stab. For a stab over an inch [deep], 1 shilling; for a stab between 2 and 3 inches, 2 shillings; for a stab over 3 inches 3 shillings.{{cite book |last=Wilkins |first=David |title=Councils and Ecclesiastical Documents Relating to Great Britain and Ireland: English church during the Anglo-Saxon period: A.D. 595-1066. |url=https://archive.org/details/councilsandeccl04wilkgoog |access-date=18 December 2014 |year=1871 |publisher=Clarendon Press |location=Oxford, UK |page=[https://archive.org/details/councilsandeccl04wilkgoog/page/n72 48]}}{{cite book |last=Duncan |first=Otis Dudley |author-link=Otis Dudley Duncan |title=Notes on social measurement: historical and critical |url=https://books.google.com/books?id=5c459mDugI0C&pg=PA87 |year=1984 |publisher=Russell Sage Foundation |location=US |isbn=978-0-87154-219-9 |page=87}}}}

An Anglo-Saxon unit of length was the barleycorn. After 1066, 1 inch was equal to 3 barleycorns, which continued to be its legal definition for several centuries, with the barleycorn being the base unit.{{cite book |title=The world of measurements: masterpieces, mysteries and muddles of metrology |url=https://archive.org/details/worldofmeasureme0000klei |url-access=registration |first=H. Arthur |last=Klein |publisher=Simon and Schuster |location=New York, US |year=1974|isbn=9780671215651 }} One of the earliest such definitions is that of 1324, where the legal definition of the inch was set out in a statute of Edward II of England, defining it as "three grains of barley, dry and round, placed end to end, lengthwise".

Similar definitions are recorded in both English and Welsh medieval law tracts.{{cite book |pages=310 |title=Northumbria's Golden Age |first1=Jane |last1=Hawkes |first2=Susan |last2=Mills |publisher=Sutton |location=UK |year=1999 |isbn=978-0-7509-1685-1}} One, dating from the first half of the 10th century, is contained in the Laws of Hywel Dda which superseded those of Dyfnwal, an even earlier definition of the inch in Wales. Both definitions, as recorded in Ancient Laws and Institutes of Wales (vol i., pp. 184, 187, 189), are that "three lengths of a barleycorn is the inch".{{cite book |title=The Traditionary Annals of the Cymry |url=https://archive.org/details/traditionaryann00willgoog |first=John |last=Williams |chapter=The civil arts – mensuration |pages=[https://archive.org/details/traditionaryann00willgoog/page/n253 243]–245 |location=Tenby, UK |publisher=R. Mason |year=1867}}

King David I of Scotland in his Assize of Weights and Measures (c. 1150) is said to have defined the Scottish inch as the width of an average man's thumb at the base of the nail, even including the requirement to calculate the average of a small, a medium, and a large man's measures.{{cite book |last1=Swinton |first1 = John| author-link1=John Swinton, Lord Swinton |title=A proposal for uniformity of weights and measures in Scotland |url=https://books.google.com/books?id=kHhbAAAAQAAJ&pg=PA134 |year=1789 |publisher=printed for Peter Hill |page=134}} However, the oldest surviving manuscripts date from the early 14th century and appear to have been altered with the inclusion of newer material.{{cite book |first1=Elizabeth |last1=Gemmill |first2=Nicholas |last2=Mayhew |title=Changing Values in Medieval Scotland: A Study of Prices, Money, and Weights and Measures |url=https://books.google.com/books?id=t1hmrzOSEagC&pg=PA113 |date=22 June 2006 |publisher=Cambridge University Press| location=UK |isbn=978-0-521-02709-0 |page=113}}

In 1814, Charles Butler, a mathematics teacher at Cheam School, recorded the old legal definition of the inch to be "three grains of sound ripe barley being taken out the middle of the ear, well dried, and laid end to end in a row", and placed the barleycorn, not the inch, as the base unit of the English Long Measure system, from which all other units were derived.{{cite book |pages=[https://archive.org/details/aneasyintroduct01butlgoog/page/n64 61] |title=An Easy Introduction to the Mathematics |url=https://archive.org/details/aneasyintroduct01butlgoog |first=Charles |last=Butler |location=Oxford, UK |publisher=Bartlett and Newman |year=1814}} John Bouvier similarly recorded in his 1843 law dictionary that the barleycorn was the fundamental measure.{{cite encyclopedia |first=John |last=Bouvier |article=Barleycorn |year=1843 |encyclopedia=A Law Dictionary: With References to the Civil and Other Systems of Foreign Law |pages=188 |location=Philadelphia, US |publisher=T. & J. W. Johnson}} Butler observed, however, that "[a]s the length of the barley-corn cannot be fixed, so the inch according to this method will be uncertain", noting that a standard inch measure was now [i.e. by 1843] kept in the Exchequer chamber, Guildhall, and that was the legal definition of the inch.

This was a point also made by George Long in his 1842 Penny Cyclopædia, observing that standard measures had since surpassed the barleycorn definition of the inch, and that to recover the inch measure from its original definition, in case the standard measure were destroyed, would involve the measurement of large numbers of barleycorns and taking their average lengths. He noted that this process would not perfectly recover the standard, since it might introduce errors of anywhere between one hundredth and one tenth of an inch in the definition of a yard.{{cite encyclopedia |page=436 |article=Weights & Measures, Standard |encyclopedia=The Penny Cyclopædia of the Society for the Diffusion of Useful Knowledge |first=George |last=Long |year=1842 |location=London, UK |publisher=Charles Knight & Co.}}

Before the adoption of the international yard and pound, various definitions were in use. In the United Kingdom and most countries of the British Commonwealth, the inch was defined in terms of the Imperial Standard Yard. The United States adopted the conversion factor 1 metre = 39.37 inches by an act in 1866.{{cite book

| first1 = Lewis V

| last1 = Judson

| title = Weights and Measures Standards of the United States - a brief history - NBS publication 447

| url = https://books.google.com/books?id=GXWfglKg11MC&q=1838+gallon+231+congress&pg=PA8

| page = 10–11

| publisher = United States Department of Commerce

| date = October 1963

}} In 1893, Mendenhall ordered the physical realization of the inch to be based on the international prototype metres numbers 21 and 27, which had been received from the CGPM, together with the previously adopted conversion factor.{{cite web |author=T. C. Mendenhall, Superintendent of Standard Weights and Measures |author-link=Thomas Corwin Mendenhall |url=http://physics.nist.gov/Pubs/SP447/app3.pdf |date=5 April 1893 |title=Appendix 6 to the Report for 1893 of the Coast and Geodetic Survey |url-status=dead |archive-url=https://web.archive.org/web/20120930180925/http://physics.nist.gov/Pubs/SP447/app3.pdf |archive-date=30 September 2012 }}

As a result of the definitions above, the U.S. inch was effectively defined as 25.4000508 mm (with a reference temperature of 68 degrees Fahrenheit) and the UK inch at 25.399977 mm (with a reference temperature of 62 degrees Fahrenheit). When Carl Edvard Johansson started manufacturing gauge blocks in inch sizes in 1912, Johansson's compromise was to manufacture gauge blocks with a nominal size of 25.4mm, with a reference temperature of 20 degrees Celsius, accurate to within a few parts per million of both official definitions. Because Johansson's blocks were so popular, his blocks became the de facto standard for manufacturers internationally,{{Cite web|url=http://mitutoyo.com/wp-content/uploads/2013/07/E12016-History-of-The-Gage-Block.pdf#page=8|title=The History of Gauge Blocks|date=2013|website=mitutoyo.com|publisher=Mitutoyo Corporation|page=8|access-date=1 February 2020}}{{Cite book|url=https://books.google.com/books?id=3rUaAQAAMAAJ&pg=PA293|title=Industrial Standardization and Commercial Standards Monthly|date=October 1943|language=en|access-date=1 February 2020|first=John|last=Gaillard|page=293}} with other manufacturers of gauge blocks following Johansson's definition by producing blocks designed to be equivalent to his.{{Cite book|url=https://books.google.com/books?id=NiEEAQAAIAAJ&pg=PA200|title=Measures for Progress. NIST Special Publication, isue 275.|last=Cochrane|first=Rexmond C.|publisher=U.S. Government Printing Office|year=1966|pages=200|language=en|lccn=65-62472}}

In 1930, the British Standards Institution adopted an inch of exactly 25.4 mm. 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,{{cite conference |url={{google books|id=WDgJAQAAMAAJ|page=RA3-PA4|plain-url=yes}} |conference=National Twenty-Eight Conference on Weights and Measures |title=The Viewpoint of industry concerned with interchangeable manufacturing toward the proposal to standardize the inch |first=Herbert B. |last=Lewis |publisher=National Bureau of Standards |location=US |year=1936 |page=4 |access-date=2 August 2012}}{{cite book |last1=Wandmacher |first1=Cornelius |last2=Johnson |first2=Arnold Ivan |title=Metric Units in Engineering--going SI: How to Use the International Systems of Measurement Units (SI) to Solve Standard Engineering Problems |url=https://books.google.com/books?id=v5AGFgpcK_wC&pg=PA265 |year=1995 |publisher=ASCE Publications|isbn=978-0-7844-0070-8|page=265}} effectively endorsing Johansson's pragmatic choice of conversion ratio.

In 1946, the Commonwealth Science Congress recommended a yard of exactly 0.9144 metres for adoption throughout the British Commonwealth. This was adopted by Canada in 1951;{{cite journal|title=Announcement on the International Yard and Pound|first=L. E.|last=Howlett|date=1 January 1959|journal=Canadian Journal of Physics|volume=37|issue=1|pages=84|doi=10.1139/p59-014|bibcode=1959CaJPh..37...84H}}{{cite book |author1=National Conference on Weights and Measures |author2=United States. Bureau of Standards |author3=National Institute of Standards and Technology (US) |author-link3=National Institute of Standards and Technology |title=Report of the ... National Conference on Weights and Measures |url=https://books.google.com/books?id=CEgJAQAAMAAJ&pg=PA45 |year=1957 |publisher=US Department of Commerce, Bureau of Standards |pages=45–6}} the United States on 1 July 1959;{{cite web |last1=Astin |first1=A.V. |last2=Karo |first2=H. A. |last3=Mueller |first3=F.H. |date=25 June 1959 |url=http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf |title=Refinement of Values for the Yard and the Pound |publisher=US Federal Register}}{{cite book |author=United States. National Bureau of Standards |author-link=National Institute of Standards and Technology |title=Research Highlights of the National Bureau of Standards |url=https://books.google.com/books?id=4aWN-VRV1AoC&pg=PA13 |year=1959 |publisher=US Department of Commerce, National Bureau of Standards |page=13}}{{cite book|author1=Lewis Van Hagen Judson|author2=United States. National Bureau of Standards|author-link2=National Institute of Standards and Technology|title=Weights and measures standards of the United States: a brief history|url=https://archive.org/details/bub_gb_o4XQ7KCv5E0C|access-date=16 September 2012|year=1976|publisher=Dept. of Commerce, National Bureau of Standards : for sale by the Supt. of Docs., U.S. Govt. Print. Off.|pages=[https://archive.org/details/bub_gb_o4XQ7KCv5E0C/page/n36 30]–1}} Australia in 1961,Statutory Rule No. 142. effective 1 January 1964;[http://www.comlaw.gov.au/Details/C2004L00578 Australian Government ComLaw Weights and Measures (National Standards) Regulations - C2004L00578] and the United Kingdom in 1963,Weights and Measures Act of 1963. effective on 1 January 1964.{{cite web |url=http://www.bailii.org/ew/cases/EWHC/Admin/2002/195.html |title=Thoburn v Sunderland City Council [2002] EWHC 195 (Admin) |date=18 February 2002 |publisher=England and Wales High Court |via=British and Irish Legal Information Institute}} The new standards gave an inch of exactly 25.4 mm, 1.7 millionths of an inch longer than the old imperial inch and 2 millionths of an inch shorter than the old US inch.{{cite web |url=http://www.npl.co.uk/reference/faqs/on-what-basis-is-one-inch-exactly-equal-to-25.4-mm-has-the-imperial-inch-been-adjusted-to-give-this-exact-fit-and-if-so-when-(faq-length) |archive-url= https://web.archive.org/web/20130126164151/http://www.npl.co.uk/reference/faqs/on-what-basis-is-one-inch-exactly-equal-to-25.4-mm-has-the-imperial-inch-been-adjusted-to-give-this-exact-fit-and-if-so-when-(faq-length) | archive-date = 26 January 2013 |title=On what basis is one inch exactly equal to 25.4 mm? Has the imperial inch been adjusted to give this exact fit and if so when? |publisher=National Physical Laboratory |date=25 March 2010 |access-date=5 April 2013}}

The United States retained the {{sfrac|1|39.37}}-metre definition for surveying, producing a 2 millionth part difference between standard and US survey inches.A. V. Astin & H. Arnold Karo, (1959), [http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf Refinement of values for the yard and the pound], Washington DC: National Bureau of Standards, republished on National Geodetic Survey web site and the Federal Register (Doc. 59-5442, Filed, 30 June 1959, 8:45 am) This is approximately {{sfrac|1|8}} inch per mile; 12.7 kilometres is exactly {{Nts|500000}} standard inches and exactly {{Nts|499999}} survey inches. This difference is substantial when doing calculations in State Plane Coordinate Systems with coordinate values in the hundreds of thousands or millions of feet.

In 2020, the National Institute of Standards and Technology announced that the U.S. survey foot would "be phased out" on 1 January 2023 and be superseded by the international foot (also known as the foot) equal to 0.3048 metres exactly, for all further applications.{{Cite web|url=https://www.nist.gov/pml/us-surveyfoot|title=U.S. Survey Foot|last=Materese|first=Robin|date=26 July 2019|website=NIST|language=en|access-date=1 February 2020}} This implies that the survey inch was replaced by the international inch.

{{Main|Roman inch|French inch}}

Before the adoption of the metric system, several European countries had customary units whose name translates into "inch". The French pouce measured roughly 27.0 mm, at least when applied to describe the calibre of artillery pieces. The Amsterdam foot (voet) consisted of 11 Amsterdam inches (duim). The Amsterdam foot is about 8% shorter than an English foot.*{{cite book

|url = {{google book|id=XYVbAAAAQAAJ|page=166|plain-url=yes}}

|title = Allereerste Gronden der Cijferkunst

|first = Jacob

|last = de Gelder

|location = The Hague

|language = nl

|year = 1824

|pages = 166

|publisher = de Gebroeders van Cleef

|trans-title=Introduction to Numeracy

|access-date = 10 April 2022}}

The now obsolete Scottish inch ({{langx|gd|òirleach}}), {{sfrac|12}} of a Scottish foot, was about 1.0016 imperial inches (about {{convert|1.0016|in|mm|disp=output only}}).{{cite web

|url =https://dsl.ac.uk/entry/snd/snds3729

|title = Dictionary of the Scots Language

|publisher = Scottish Language Dictionaries

|location = Edinburgh

|access-date =22 January 2020}}

{{div col|colwidth=23em}}

• English units
• Square inch and Cubic inch
• International yard and pound
• Anthropic units
• Pyramid inch
• Digit and Line

{{Div col end}}

{{Notelist|2}}

{{Reflist|30em}}

• {{Citation | last = Attenborough | first = F. L. | author-link = Frederick Attenborough | title = The Laws of the Earliest English Kings | edition = Llanerch Press Facsimile Reprint 2000 | location = Cambridge | publisher = Cambridge University Press | year = 1922 | isbn = 978-1-86143-101-1 |url=https://archive.org/details/cu31924070153519 |access-date= 11 July 2018}}

{{Imperial units}}

{{United States Customary Units}}

{{Authority control}}

Category:Customary units of measurement in the United States

Category:Imperial units

Category:Units of length

Category:Obsolete Scottish units of measurement

fy:Tomme (lingtemaat)