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The foot (standard symbol: ft) is a unit of length in the imperial units and United States customary systems of metrology. The prime symbol, , is commonly used to represent the foot. In both customary and imperial units, one foot comprises 12 , and one yard comprises three feet. Since an international agreement in 1959, the foot is defined as equal to exactly 0.3048Metre. The most common plural of foot is feet. 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".
Historically, the "foot" was a part of many local systems of units, including the Greek, Roman, Chinese, French, and English systems. It varied in length from country to country, from city to city, and sometimes from trade to trade. Its length was usually between and and was generally, but not always, subdivided into twelve inches or 16 digits.
The United States is the only industrialized country that uses the (international) foot in preference to the meter in its commercial, engineering, and standards activities. The foot is legally recognized in the United Kingdom; road distance signs must 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.Alder, Ken (2002). The Measure of all Things—The Seven-Year-Odyssey that Transformed the World. London: Abacus. The foot is recognized as an alternative expression of length in Canada. Weights and Measures Act , 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). Both the UK and Canada have partially Metrication their units of measurement. The measurement of altitude in international aviation (the flight level unit) is one of the few areas where the foot is used outside the English-speaking world.
Archaeologists believe that in the past, the people of Egypt, India, and Mesopotamia preferred the cubit, while the people of Ancient Rome, Ancient Greece, and China preferred the foot. Under the Harappan linear measures, Indus cities during the Bronze Age used a foot of and a cubit of .Kenoyer JM (2010) "Measuring the Harappan world," in Morley I & Renfrew C (edd) The Archaeology of Measurement, 117; The Egyptian equivalent of the foot—a measure of four palms or 16 digits—was known as the djeser and has been reconstructed as about .
The Greek foot (πούς, pous) had a length of of a stadion, one stadion being about ; therefore a foot was about . Its exact size varied from city to city and could range between and , but lengths used for temple construction appear to have been about to .
The standard Roman foot (pes) was normally about ,Hosch, William L. (ed.) (2010) The Britannica Guide to Numbers and Measurement New York, NY: Britannica Educational Publications, 1st edition. , p.206 but in some provinces, particularly Germania Inferior, the so-called pes Drusianus (foot of Nero Claudius Drusus) was sometimes used, with a length of about . (In reality, this foot predated Drusus.)Oswald Ashton Wentworth Dilke (1987). 9780520060722, University of California Press. . ISBN 9780520060722 Originally both the Greeks and the Romans subdivided the foot into 16 digits, but in later years, the Romans also subdivided the foot into 12 unciae (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 790 Charlemagne attempted to reform the units of measure in his domains. His units of length were based on the toise and in particular the toise de l'Écritoire, the distance between the fingertips of the outstretched arms of a man. The toise has 6 pieds (feet) each of . He was unsuccessful in introducing a standard unit of length throughout his realm: an analysis of the measurements of Charlieu Abbey shows that during the 9th century the Roman foot of was used; when it was rebuilt in the 10th century, a foot of about was used. At the same time, monastic buildings used the Carolingian foot of .
The procedure for verification of the foot as described in the 16th century posthumously published work by Jacob Köbel in his book Geometrei. Von künstlichem Feldmessen und absehen is:
The measures of Iron Age Britain are uncertain, and proposed reconstructions such as the megalithic yard are controversial. Later Welsh mythology credited Dyfnwal Moelmud with the establishment of their units, including a foot of 9 inches. The Belgic or North German foot of was introduced to England either by the Belgae during their invasions prior to the Roman conquest of Britain (AD 43) or by the Anglo-Saxons in the 5th and 6th centuries.
Roman units were introduced following their conquest. After the Roman withdrawal and the Saxon 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 the barleycorn, but by as early as 950 the English kings seem to have (ineffectually) ordered measures to be based upon an iron yardstick at Winchester and then London. Henry I was said to have ordered a new standard to be based upon the length of his own arm and, by the act concerning the Composition of Yards and Perches traditionally credited to Edward I or Edward II, the statute foot was a different measure, exactly of the old (Belgic) foot. The barleycorn, inch, ell, and yard were likewise shrunk, while rods and remained the same. The ambiguity over the length of the mile was resolved by the 1593 Act 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.
The Institute of Electrical and Electronics Engineers standard symbol for a foot is "ft". In some cases, the foot is denoted by a prime, often approximated by an apostrophe, and the inch by a double prime; for example, 2feet 4 inches is sometimes denoted 2′4″.
On December 31, 2022, the National Institute of Standards and Technology, the National Geodetic Survey, and the United States Department of Commerce deprecated use of the US survey foot and recommended conversion to either the meter or the international foot (0.3048 m). "Measuring Unit Change Coming in 2022", National Geodetic Survey, June 14, 2019. However, the historic relevance of the US survey foot persists, as the Federal Register notes:
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. "State Plane Coordinate System", National Geodetic Survey, May 4, 2019.
In 1799 the meter became the official unit of length in France. This was not fully enforced, and in 1812 Napoleon introduced the system of mesures usuelles which restored the traditional French measurements in the retail trade, but redefined them in terms of metric units. The foot, or pied métrique, was defined as one third of a meter. This unit continued in use until 1837.
In southwestern Germany in 1806, the Confederation of the Rhine was founded and three different reformed feet were defined, all of which were based on the metric system:
Many of these standards were peculiar to a particular city, especially in Germany (which, before German 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 11 pouces 2.6 lignes (French inches and lines) by Jean Picard, 11 pouces 3.11 lignes by Nevil Maskelyne, and 11 pouces 3 lignes by D'Alembert.
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 the mesures usuelles under Napoleon and the German Empire adopted the metric system in 1871.
The palm (typically 200–280 mm, ie. 7 to 11 inches) was used in many Mediterranean cities instead of the foot. Horace Doursther, whose reference was published 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).
| Vienna | Austria | Wiener Fuß | 316.102 | |
| Tyrol | Austria | Fuß | 334.12 | |
| Ypres | Belgium | voet | 273.8 | |
| Bruges | Belgium | voet | 274.3 | |
| Brussels | Belgium | voet | 275.75 | |
| Hainaut | Belgium | pied | 293.39 | |
| Liège | Belgium | pied | 294.70 | |
| Kortrijk | Belgium | voet | 297.6 | |
| Aalst | Belgium | voet | 277.2 | |
| Mechelen | Belgium | voet | 278.0 | |
| Leuven | Belgium | voet | 285.5 | |
| Tournai | Belgium | pied | 297.77 | |
| Antwerp | Belgium | voet | 286.8 | |
| China | China | tradesman's foot | 338.3 | |
| China | China | mathematician's foot | 333.2 | |
| China | China | builder's foot | 322.8 | |
| China | China | surveyor's foot | 319.5 | |
| Moravia | Czech Republic | stopa | 295.95 | |
| Prague | Czech Republic | stopa | 296.4 | (1851) Bohemian foot or shoe |
| 301.7 | (1759) Quoted as "11 pouces lignes" | |||
| Denmark | Denmark | fod | 313.85 | Until 1835, thereafter the Prussian foot |
| 330.5 | (1759) Quoted as " lignes larger than the pied of" | |||
| France | France | pied du roi | 324.84 | The original meter was computed using pre-metric French units. |
| Angoulême | France | pied d'Angoulême | 347.008 | |
| Bordeaux (urban) | France | pied de ville de Bordeaux | 343.606 | |
| Bordeaux (rural) | France | pied de terre de Bordeaux | 357.214 | |
| Strasbourg | France | pied de Strasbourg | 294.95 | |
| Württemberg | Germany | Fuß | 286.49 | |
| Hanover | Germany | Fuß | 292.10 | |
| Augsburg | Germany | römischer Fuß | 296.17 | |
| Nuremberg | Germany | Fuß | 303.75 | |
| Meiningen-Hildburghausen | Germany | Fuß | 303.95 | |
| Oldenburg | Germany | römischer Fuß | 296.41 | |
| Weimar | Germany | Fuß | 281.98 | |
| Lübeck | Germany | Fuß | 287.62 | |
| Aschaffenburg | Germany | Fuß | 287.5 | |
| Darmstadt | Germany | Fuß | 287.6 | Until 1818, thereafter the Hessen "metric foot" |
| Bremen | Germany | Fuß | 289.35 | |
| Rhineland | Germany | Fuß | 313.7 | |
| Berlin | Germany | Fuß | 309.6 | |
| Hamburg | Germany | Fuß | 286.8 | |
| Bavaria | Germany | Fuß | 291.86 | |
| Aachen | Germany | Fuß | 282.1 | |
| Leipzig | Germany | Fuß | 282.67 | |
| Dresden | Germany | Fuß | 283.11 | |
| Saxony | Germany | Fuß | 283.19 | |
| Prussia | Germany, Poland, Russia etc. | Rheinfuß | 313.85 | |
| Frankfurt am Main | Germany | Fuß | 284.61 | |
| Venice & Lombardy | Italy | 347.73 | ||
| Turin | Italy | 323.1 | ||
| Rome | Italy | piede romano | 297.896 | |
| Riga | Latvia | pēda | 274.1 | |
| Malta | Malta | pied | 283.7 | |
| Utrecht | Netherlands | voet | 272.8 | |
| Amsterdam | Netherlands | voet | 283.133 | Divided into 11 duimen (inches, ) |
| Netherlands | voet | 285.0 | ||
| 's-Hertogenbosch | Netherlands | voet | 287.0 | |
| Gelderland | Netherlands | voet | 292.0 | |
| Bloois | Netherlands | voet | 301.0 | |
| Schouw | Netherlands | voet | 311.0 | |
| Rotterdam | Netherlands | voet | 312.43 | |
| Rijnland | Netherlands | voet | 314.858 | |
| Norway | Norway | fot | 313.75 | (1824–1835)The Norwegian fot was defined in 1824 as the length of a (theoretical) pendulum that would have a period of seconds at 45° from the equator. Thereafter as for Sweden. |
| Warsaw | Poland | stopa | 297.8 – Information copied from | Until 1819 |
| 288.0 | (From 1819) Polish stopa | |||
| Lisbon | Portugal | pé | 330.0 | (From 1835)Prior to 1835, the pé 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. |
| South Africa | South Africa | Cape foot | 314.858 | Originally equal to the Rijnland foot; redefined as 1.033 English feet in 1859. |
| Burgos and Castile | Spain | pie de Burgos/ Castellano | 278.6 | (1759) Quoted as "122.43 lignes" |
| Toledo | Spain | pie | 279.0 | (1759) Quoted as "10 pouces 3.7 lignes"The source document used pre-metric French units (pied, pouce and ligne). |
| Sweden | Sweden | fot | 296.9 | = 12 tum (inches). The Swedish fot was also used in Finland (jalka). |
| Zürich | Switzerland | 300.0 | ||
| Galicia | Ukraine, Poland | stopa galicyjska | 296.96 | Part of Austria–Hungary before World War I |
| Scotland | United Kingdom | 305.287 | The Scots foot ceased to be legal after the Act of Union in 1707. |
In Belgium, the words pied (French) and voet (Dutch) would have been used interchangeably.
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