Thefoot (standard symbol:ft)[1][2] is aunit oflength in theBritish imperial andUnited States customary systems ofmeasurement. Theprime symbol,′, is commonly used to represent the foot.[3] In both customary and imperial units, one foot comprises 12 inches, and oneyard comprises three feet. Sincean international agreement in 1959, the foot is defined as equal to exactly 0.3048meters. The most common plural offoot isfeet. However, the singular form may be used like a plural when it is preceded by a number, as in "that man is six foot tall".[4]
Historically, the "foot" was a part of many local systems of units, including theGreek,Roman,Chinese,French, andEnglish systems. It varied in length from country to country, from city to city, and sometimes from trade to trade. Its length was usually between 250 mm (9.8 in) and 335 mm (13.2 in) and was generally, but not always, subdivided into twelve inches or 16 digits.
The United States is the onlyindustrialized country that uses the (international) foot in preference to the meter in its commercial, engineering, and standards activities.[5] The foot is legally recognized in the United Kingdom; road distance signsmust use imperial units (however, distances on road signs are marked in miles or yards, not feet; bridge clearances are given in meters as well as feet and inches), while its usage is widespread among the British public as a measurement of height.[6][7] The foot is recognized as an alternative expression of length in Canada.[8] Both the UK and Canada have partiallymetricated their units of measurement. The measurement ofaltitude in internationalaviation (theflight level unit) is one of the few areas where the foot is used outside the English-speaking world.
Determination of the rod, using the length of the left foot of 16 randomly chosen people coming from church service. Woodcut published in the bookGeometrey byJakob Köbel (Frankfurt,c. 1535).
Historically, the human body has been used to provide the basis for units of length.[9] Thefoot of an adult European-American male is typically about 15.3% of his height,[10] giving a person of 175 cm (5 ft 9 in) a foot-length of about 268 mm (10.6 in), on average.
Archaeologists believe that in the past, the people ofEgypt,India, andMesopotamia preferred thecubit, while the people ofRome,Greece, andChina preferred the foot[citation needed]. Under theHarappan linear measures,Indus cities during the Bronze Age used a foot of 13.2 inches (335 mm) and a cubit of 20.8 inches (528 mm).[11] The Egyptian equivalent of the foot—a measure of four palms or 16 digits—was known as thedjeser and has been reconstructed as about 30 cm (11.8 in).
The Greek foot (πούς,pous) had a length of1/600 of astadion,[12] one stadion being about 181.2 m (594 ft);[13] therefore a foot was about 302 mm (11.9 in). Its exact size varied from city to city and could range between 270 mm (10.6 in) and 350 mm (13.8 in), but lengths used for temple construction appear to have been about 295 mm (11.6 in) to 325 mm (12.8 in).
Thestandard Roman foot (pes) was normally about 295.7 mm (11.6 in),[14] but in some provinces, particularlyGermania Inferior, the so-calledpes Drusianus (foot ofNero Claudius Drusus) was sometimes used, with a length of about 334 mm (13.1 in). (In reality, this foot predated Drusus.)[15][16] Originally both the Greeks and the Romans subdivided the foot into 16digits, but in later years, the Romans also subdivided the foot into 12unciae (from which both the English words "inch" and "ounce" are derived). After the fall of the Roman Empire, some Roman traditions were continued but others fell into disuse. In 790Charlemagne attempted to reform the units of measure in his domains. His units of length were based on thetoise and in particular thetoise de l'Écritoire, the distance between the fingertips of the outstretched arms of a man.[17] Thetoise has 6pieds (feet) each of 326.6 mm (12.9 in). He was unsuccessful in introducing a standard unit of length throughout his realm: an analysis of the measurements ofCharlieu Abbey shows that during the 9th century the Roman foot of 296.1 mm (11.66 in) was used; when it was rebuilt in the 10th century, a foot of about 320 mm (12.6 in)[a] was used. At the same time, monastic buildings used the Carolingian foot of 340 mm (13.4 in).[a][18]
The procedure for verification of the foot as described in the 16th century posthumously published work byJacob Köbel in his bookGeometrei. Von künstlichem Feldmessen und absehen is:[19][20]
Stand at the door of a church on a Sunday and bid 16 men to stop, tall ones and small ones, as they happen to pass out when the service is finished; then make them put their left feet one behind the other, and the length thus obtained shall be a right and lawfulrood to measure and survey the land with, and the 16th part of it shall be the right and lawful foot.
TheNeolithiclong foot, first proposed by archeologistsMike Parker Pearson and Andrew Chamberlain, is based upon calculations from surveys ofPhase 1 elements at Stonehenge. They found that the underlying diameters of the stone circles had been consistently laid out using multiples of a base unit amounting to 30long feet, which they calculated to be 1.056 of a moderninternational foot (thus 12.672 inches or 0.3219 m). Furthermore, this unit is identifiable in the dimensions of some stonelintels at the site, and in the diameter of the "southern circle" at nearbyDurrington Walls. Evidence that this unit was in widespread use across southern Britain is available from theFolkton Drums fromYorkshire (Neolithic artifacts made from chalk with circumferences that exactly divide asintegers into ten long feet) and a similar object, theLavant drum, excavated atLavant, Sussex, again with a circumference divisible as a whole number into ten long feet.[21]
Roman units were introduced following their conquest. After theRoman withdrawal and theSaxon invasions, the Roman foot continued to be used in the construction crafts, while the Belgic foot was used for land measurement. Both the Welsh and Belgic feet seem to have been based on multiples of thebarleycorn, but by as early as 950 the English kings seem to have (ineffectually) ordered measures to be based upon an iron yardstick atWinchester and thenLondon.Henry I was said to have ordered a new standard to be based upon the length of his own arm and, by thec. 1300 act concerning theComposition of Yards and Perches[22] traditionally credited toEdward I orEdward II, the statute foot was a different measure, exactly10/11 of the old (Belgic) foot. The barleycorn, inch,ell, andyard were likewise shrunk, whilerods andfurlongs remained the same.[23] The ambiguity over the length of themile was resolved by the 1593Act against Converting of Great Houses into Several Tenements and for Restraint of Inmates and Inclosures in and near about the City of London and Westminster, which codified the statute mile as comprising 5,280 feet. The 1959 adoption of the international foot completed a redefinition of the foot in terms of the meter.
Theinternational yard and pound agreement of July 1959 defined the length of the international yard in the United States and countries of theCommonwealth of Nations as exactly 0.9144meters. Consequently, since a foot is one third of a yard, the international foot is defined as exactly 0.3048 meters. This was 2 ppm shorter than the previous US definition and 1.7 ppm longer than the previous British definition.[24] The 1959 agreement concluded a series of step-by-step events, set off in particular by theBritish Standards Institution's adoption of a scientific standard inch of 25.4millimeters in 1930.
InImperial units, the foot was defined as1/3 yard, with the yard being realized as a physical standard (separate from the standard meter). The yard standards of the differentCommonwealth countries were periodically compared with one another.[26] The value of the United Kingdom primary standard of the yard was determined in terms of the meter by theNational Physical Laboratory in 1964 to be0.9143969 m,[27] implying a pre-1959 UK foot of0.3047990 m. The UK adopted the international yard for all purposes through theWeights and Measures Act 1963, effective January 1, 1964.[28]
When the international foot was defined in 1959, a great deal of survey data was already available based on the former definitions, especially in the United States and in India. The small difference between the survey foot and the international foot would not be detectable on a survey of a small parcel but becomes significant for mapping or when thestate plane coordinate system (SPCS) is used in the US, because the origin of the system may be hundreds of thousands of feet (hundreds of miles) from the point of interest. Hence the previous definitions continued to be used for surveying in the United States and India for many years and are denotedsurvey feet to distinguish them from the international foot. The United Kingdom was unaffected by this problem, as theretriangulation of Great Britain (1936–62) had been done in meters.
In the United States, the foot was defined as 12 inches, with the inch being defined by theMendenhall Order of 1893 via 39.37 inches = 1 m (making a US foot exactly1200/3937meters, approximately0.30480061 m).[29][30]
The date of December 31, 2022, was selected to accompany the modernization of theNational Spatial Reference System (NSRS) byNOAA's National Geodetic Survey (NGS). The reason for associating the deprecation of the U.S. survey foot with the modernization of the NSRS is that the biggest impact of the uniform adoption of the international foot will be for users of the NSRS, due to very large coordinate values currently given in U.S. survey feet in many areas of the U.S. Impacts related to the change to international feet will be minimized if a transition occurs concurrently with others [sic] changes in the NSRS. ...
The difference in timelines will have no effect on users of the existing NSRS (National Spatial Reference System), because NGS (NOAA's National Geodetic Survey)will continue to support the U.S. survey foot for components of the NSRS where it is used now and in the past [emphasis added]. In other words, to minimize disruption in the use of U.S. survey foot for existing NSRS coordinate systems, the change will apply only to the modernized NSRS.
State legislation is also important for determining the conversion factor to be used for everyday land surveying and real estate transactions, although the difference (two ppm) is of no practical significance given the precision of normal surveying measurements over short distances (usually much less than a mile). Out of 50 states and six other jurisdictions, 40 have legislated that surveying measures should be based on the US survey foot, six have legislated that they be made on the basis of the international foot, and ten have not specified.[34]
The Indian survey foot is defined as exactly0.3047996 m,[35] presumably derived from a measurement of the previous Indian standard of the yard. The current National Topographic Database of theSurvey of India is based on the metricWGS-84datum,[36] which is also used by theGlobal Positioning System.
AnISO 2848 measure of 3 basic modules (30 cm) is called a "metric foot",[citation needed] but there were earlier distinct definitions of a metric foot duringmetrication in France and Germany.
In 1799 the meter became the official unit of length inFrance. This was not fully enforced, and in 1812Napoleon introduced the system ofmesures usuelles which restored the traditional French measurements in the retail trade, but redefined them in terms of metric units. The foot, orpied métrique, was defined as one third of a meter. This unit continued in use until 1837.[38]
In southwestern Germany in 1806, theConfederation of the Rhine was founded and three differentreformed feet were defined, all of which were based on the metric system:[39]
Prior to the introduction of the metric system, many European cities and countries used the foot, but it varied considerably in length: thevoet inYpres, Belgium, was 273.8 mm (10.78 in) while thepiede in Venice was 347.73 mm (13.690 in). Lists of conversion factors between the various units of measure were given in many European reference works including:
Many of these standards were peculiar to a particular city, especially in Germany (which, beforeGerman unification in 1871, consisted of many kingdoms, principalities, free cities and so on). In many cases the length of the unit was not uniquely fixed: for example, the English foot was stated as 11pouces 2.6lignes (French inches and lines) byPicard, 11pouces 3.11lignes byMaskelyne, and 11pouces 3lignes byD'Alembert.[47]
Most of the various feet in this list ceased to be used when the countries adopted the metric system. The Netherlands and modern Belgium adopted the metric system in 1817, having used themesures usuelles under Napoleon[48] and theGerman Empire adopted the metric system in 1871.[49]
Thepalm (typically 200–280 mm, ie. 77/8 to 111/32 inches) was used in many Mediterranean cities instead of the foot. Horace Doursther, whose reference was published[clarification needed] in Belgium which had the smallest foot measurements, grouped both units together, while J. F. G. Palaiseau devoted three chapters to units of length: one for linear measures (palms and feet); one for cloth measures (ells); and one for distances traveled (miles and leagues).[citation needed]
^abcdThe source document used pre-metric French units (pied,pouce andligne).
^The original meter was computed using pre-metric French units.
^The Norwegianfot was defined in 1824 as the length of a (theoretical) pendulum that would have a period of12/38 seconds at 45° from the equator.
^Prior to 1835, thepé or foot was not used in Portugal; instead a palm was used. In 1835 the size of the palm was increased from 217.37 mm (according to Palaiseau) to 220 mm.
^The Scots foot ceased to be legal after theAct of Union in 1707.
International Organization for Standardization (ISO)-definedintermodal containers for efficient global freight/cargo shipping, were defined using feet rather than meters for their leading outside (corner) dimensions. All ISO-standard containers to this day are eight feet (2.4 m) wide, and their outer heights and lengths are also primarily defined in, or derived from feet. Quantities of global shipping containers are still primarily counted intwenty-foot equivalent units (TEUs).
Everyday global (civilian) air traffic and aviation continues to be controlled inflight levels (flying altitudes) separated by thousands of feet (although typically read out in hundreds; for example, "flight level 330" means 33,000 feet (10,000 m) in altitude.
The length of the (international) foot corresponds to a human foot withshoe size of 13 (UK), 14 (US male), 15.5 (US female) or 48 (EU sizing).[58][better source needed]
In measurement, the term "linear foot" (sometimes incorrectly referred to as "lineal foot") refers to the number of feet in a length of material (such as lumber or fabric) without regard to the width; it is used to distinguish fromsurface area insquare foot.[59]
^Alder, Ken (2002). The Measure of all Things—The Seven-Year-Odyssey that Transformed the World. London: Abacus.
^Weights and Measures ActArchived December 28, 2014, at theWayback Machine, accessed January 2012, Act current to January 18, 2012. Basis for units of measurement 4.(1) All units of measurement used in Canada shall be determined on the basis of the International System of Units established by the General Conference of Weights and Measures. (...) 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).
^Kenoyer JM (2010) "Measuring the Harappan world," in Morley I & Renfrew C (edd) The Archaeology of Measurement, 117;"Archived copy"(PDF). Archived fromthe original(PDF) on June 26, 2015. RetrievedJanuary 11, 2015.{{cite web}}: CS1 maint: archived copy as title (link)
^Sutherland, Elizabeth R (May 1957). "Feet and dates at Charlieu".Journal of the Society of Architectural Historians.16 (2):2–5.doi:10.2307/987740.JSTOR987740.
^Chicago Manual of Style (17th ed.). University of Chicago Press. 2017. ¶ 10.66.
^See, for example,Report on the Comparisons of the Parliamentary Copies of the Imperial Standards with the Imperial Standard Yard and the Imperial Standard Pound and with each other during the Years 1947 to 1948 (H.M.S.O., London, 1950).Report on the Comparisons of the Parliamentary Copies of the Imperial Standards with each other during the Year 1957 (H.M.S.O., London, 1958).
^Denis Février."Un historique du mètre" (in French). Ministère de l'Économie, des Finances et de l'Industrie.Archived from the original on February 28, 2011. RetrievedMarch 10, 2011.
^abcdefghJacob de Gelder (1824).Allereerste Gronden der Cijferkunst [Introduction to Numeracy] (in Dutch). 's-Gravenhage (The Hague) and Amsterdam: de Gebroeders van Cleef. pp. 163–176. RetrievedMarch 2, 2011.
^de Gelder, Jacob (1824).Allereerste Gronden der Cijferkunst [Introduction to Numeracy] (in Dutch). The Hague and Amsterdam: De Gebroeders van Cleef. pp. 155–157. RetrievedMarch 2, 2011.
^Dreizler, Andreas; et al. (April 20, 2009)."Metrologie"(PDF) (in German). Technical University of Darmstadt. RetrievedMarch 28, 2011.[dead link]
^abcdefgh"Maten en gewichten" [Weights and measures] (in Dutch). Vlaamse Vereniging voor Familiekunde (Flemish Association for Family History). 2011. Archived fromthe original on April 25, 2012. RetrievedOctober 24, 2011.
^abcdefghijklRose, Joshua (1900).Pattern Makers Assistant (9th ed.). New York: D. van Nostrand Co. p. 264.
^"Les anciennes unités et leurs équivalences" [Old units and their equivalences] (in French). Le Cybergroupe Généalogique de Charente Poitevine. 2011.Archived from the original on July 20, 2011. RetrievedFebruary 25, 2011.
^abcdeGuilhiermoz, P (1913). "De l'équivalence des anciennes mesures. A propos d'une publication récente" [Values of ancient measures quoted in recent publications].Bibliothèque de l'École des chartes (in French).74:267–328.doi:10.3406/bec.1913.448498.
^halbo, leif (July 21, 2005). "Mål, vekt og norsk selvstendighet" [Dimensions, weight and Norwegian independence].Aftenposten (in Norwegian).
^Melissa (March 30, 2016)."Why are shoe sizes as they are?".Today I found out. (12×3=36. US(m): 36−22=14, UK: 36−23=13, EU:30.5×1.5=45.75 then +2 "for comfort" plus rounding = 48)
