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The foot ( feet), standard symbol: ft, is a unit of length in the British imperial and United States customary systems of measurement. The prime symbol, , is a customarily used alternative symbol. Since the
International Yard and Pound Agreement 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. T ...
of 1959, one foot is defined as 0.3048 
meters The metre (British spelling) or meter (American spelling; see spelling differences) (from the French unit , from the Greek noun , "measure"), symbol m, is the primary unit of length in the International System of Units (SI), though its pr ...
exactly. In both customary and imperial units, one foot comprises 12  inches and one yard comprises three feet. Historically the "foot" was a part of many local systems of units, including the Greek,
Roman Roman or Romans most often refers to: * Rome, the capital city of Italy * Ancient Rome, Roman civilization from 8th century BC to 5th century AD *Roman people, the people of ancient Rome *''Epistle to the Romans'', shortened to ''Romans'', a lett ...
, Chinese,
French French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...
, and
English English usually refers to: * English language * English people English may also refer to: Peoples, culture, and language * ''English'', an adjective for something of, from, or related to England ** English national ...
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 and 335 mm and was generally, but not always, subdivided into 12 inches or 16  digits. The United States is the only industrialized nation that uses the international foot and the survey foot (a customary unit of length) in preference to the meter in its commercial, engineering, and standards activities. The foot is legally recognized in the United Kingdom; road signs ''must'' use imperial units (however, distances on road signs are always marked in miles or yards, not feet), while its usage is widespread among the British public as a measurement of height. The foot is recognized as an alternative expression of length in Canada officially defined as a unit derived from the meter although both the U.K. and Canada have partially metricated their units of measurement. The measurement of altitude in international aviation is one of the few areas where the foot is used outside the English-speaking world. The length of the international foot corresponds to a human foot with
shoe size A shoe size is an indication of the fitting size of a shoe for a person. There are a number of different shoe-size systems used worldwide. While all shoe sizes use a number to indicate the length of the shoe, they differ in exactly what they me ...
of 13 (UK), 14 (US male), 15.5 (US female) or 48 (EU sizing).


Historical origin

Historically, the human body has been used to provide the basis for units of length. The foot of an adult Caucasian male is typically about 15.3% of his height, giving a person of a foot-length of about , on average. Archaeologists believe that, in the past, the people of
Egypt Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a List of transcontinental countries, transcontinental country spanning the North Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via a land bridg ...
,
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
, and Mesopotamia preferred the cubit, while the people of Rome,
Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders wi ...
, and
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
preferred the foot. Under the Harappan linear measures, Indus cities during the Bronze Age used a foot of 333.5 mm (13.2 in) and a cubit of 528.3 mm (20.8 in). The Egyptian equivalent of the foot—a measure of four palms or 16 digits—was known as the and has been reconstructed as about . The Greek foot (, ) had a length of of a stadion, one stadion being about ; therefore a foot was, at the time, 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 former was close to the size of the Roman foot. The standard
Roman foot Roman or Romans most often refers to: *Rome, the capital city of Italy * Ancient Rome, Roman civilization from 8th century BC to 5th century AD *Roman people, the people of ancient Rome *''Epistle to the Romans'', shortened to ''Romans'', a lette ...
() was normally about (97% of today's measurement),Hosch, William L. (ed.) (2010
''The Britannica Guide to Numbers and Measurement''
New York, NY: Britannica Educational Publications, 1st edition. , p.206
but, in the provinces, the so-called (foot of Nero Claudius Drusus) was used, with a length of about . (In reality, this foot predated Drusus.) 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 (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 AD 790 Charlemagne attempted to reform the units of measure in his domains. His units of length were based on the and in particular the , the distance between the fingertips of the outstretched arms of a man. The has 6 (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 The original reference was given in a round number of centimeters 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 is:


England

The Neolithic long foot, first proposed by archeologists Mike Parker Pearson and Andrew Chamberlain, is based upon calculations from surveys of Phase 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 30 long feet, which they calculated to be 1.056 of a modern international foot (thus 12.672 inches or 0.3219 m). Furthermore, this unit is identifiable in the dimensions of some stone
lintels A lintel or lintol is a type of beam (a horizontal structural element) that spans openings such as portals, doors, windows and fireplaces. It can be a decorative architectural element, or a combined ornamented structural item. In the case of ...
at the site and in the diameter of the "southern circle" at nearby Durrington Walls. Evidence that this unit was in widespread use across southern Britain is available from the Folkton Drums from Yorkshire ( neolithic artifacts, made from chalk, with circumferences that exactly divide as integers into ten long feet) and a similar object, the Lavant drum, excavated at Lavant, Sussex, again with a circumference divisible as a whole number into ten long feet. The measures of Iron Age Britain are uncertain and proposed reconstructions such as the Megalithic Yard are controversial. Later Welsh legend 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 Belgic Celts during their invasions prior to the Romans or by the
Anglo-Saxons The Anglo-Saxons were a cultural group who inhabited England in the Early Middle Ages. They traced their origins to settlers who came to Britain from mainland Europe in the 5th century. However, the ethnogenesis of the Anglo-Saxons happened ...
in the 5th and 6th century. Roman units were introduced following their invasion in AD 43. Following the Roman withdrawal and 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 London is the capital and List of urban areas in the United Kingdom, largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary dow ...
.
Henry I Henry I may refer to: 876–1366 * Henry I the Fowler, King of Germany (876–936) * Henry I, Duke of Bavaria (died 955) * Henry I of Austria, Margrave of Austria (died 1018) * Henry I of France (1008–1060) * Henry I the Long, Margrave of the N ...
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 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 furlongs remained the same. The ambiguity over the state 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 differences among the various physical standard yards around the world, revealed by increasingly powerful microscopes, eventually led to the 1959 adoption of the international foot defined in terms of the meter.


Definition


International foot

The international yard and pound agreement of July 1959 defined the length of the international yard in the United States and countries of the Commonwealth of Nations as exactly 0.9144 meters. Consequently (since a foot is one-third of a yard), the international foot is defined to be equal to exactly 0.3048 meters. This was 2  ppm shorter than the previous U.S. definition and 1.7 ppm longer than the previous British definition. The 1959 agreement concluded a series of step-by-step events, set off in particular by the British Standards Institution's adoption of a scientific standard inch of 25.4 millimetres in 1930.


Symbol

The IEEE standard symbol for a foot is "ft". In some cases, the foot is denoted by a
prime A prime number (or a prime) is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways ...
, often approximated by an apostrophe, and the inch by a double prime; for example, 2feet 4 inches is sometimes denoted as 2′4″.


Imperial units

In Imperial units, the foot was defined as  yard, with the yard being realized as a physical standard (separate from the standard meter). The yard standards of the different Commonwealth countries were periodically compared with one another. The value of the United Kingdom primary standard of the yard was determined in terms of the meter by the National Physical Laboratory in 1964 to be , implying a pre-1959 UK foot of . The UK adopted the international yard for all purposes through the Weights and Measures Act 1963, effective January 1, 1964.


Survey foot

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 India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
. 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 the
state plane coordinate system The State Plane Coordinate System (SPCS) is a set of 124 geographic zones or coordinate systems designed for specific regions of the United States. Each state contains one or more state plane zones, the boundaries of which usually follow county li ...
(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 denoted survey feet to distinguish them from the international foot. The United Kingdom was unaffected by this problem, as the
retriangulation of Great Britain __NOTOC__ The retriangulation of Great Britain was a triangulation project carried out between 1935 and 1962 that sought to improve the accuracy of maps made of Great Britain. Data gathered from the retriangulation replaced data gathered during ...
(1936–62) had been done in meters.


U.S. survey foot

In the United States, the foot was defined as 12 inches, with the inch being defined by the Mendenhall Order of 1893 as 39.37 inches = 1 m (making a US foot exactly meters, approximately ). Out of 50 states and six other jurisdictions, 40 have legislated that surveying measures should be based on the U.S. survey foot, six have legislated that they be made on the basis of the international foot, and ten have not specified. 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 parts per million) is of no practical significance given the precision of normal surveying measurements over short distances (usually much less than a mile). The National Institute of Standards and Technology,
National Geodetic Survey The National Geodetic Survey (NGS) is a United States federal agency that defines and manages a national coordinate system, providing the foundation for transportation and communication; mapping and charting; and a large number of applications ...
, and the United States Department of Commerce are phasing out the US survey foot beginning in 2023. However, its relevance may persist, as the Federal Register Notice says: :"The date of December 31, 2022, was selected to accompany the modernization of the National Spatial Reference System (NSRS) by NOAA'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 changes in the NSRS." :"The difference 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.'' 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."


Indian survey foot

The Indian survey foot is defined as exactly , presumably derived from a measurement of the previous Indian standard of the yard. The current National Topographic Database of the Survey of India is based on the metric WGS-84
datum In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted. ...
, which is also used by the Global Positioning System.


Historical use


Metric foot

An ISO 2848 measure of 3 basic modules (30 cm) is called a " metric foot", but there were earlier distinct definitions of a metric foot during metrication in France and Germany.


France

In 1799 the meter became the official unit of length in
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
. This was not fully enforced, and in 1812 Napoleon introduced the system of ''
mesures usuelles Mesures usuelles (, ''customary measurements'') were a French system of measurement introduced by Napoleon I in 1812 to act as compromise between the metric system and traditional measurements. The system was restricted to use in the retail indu ...
'' 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.


Germany

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: *In Hesse, the ''Fuß'' (foot) was redefined as 25 cm. *In Baden, the ''Fuß'' was redefined as 30 cm. *In the Palatinate, the ''Fuß'' was redefined as being  cm (as in France).


Other obsolete feet

Prior to the introduction of the metric system, many European cities and countries used the foot, but it varied considerably in length: the ''voet'' in Ypres, Belgium, was 273.8 millimeters (10.78in) while the piede in Venice was 347.73 millimeters (13.690in). Lists of conversion factors between the various units of measure were given in many European reference works including: *Traité, Paris – 1769 *Palaiseau – Bordeaux: 1816 *de Gelder, Amsterdam and The Hague – 1824 *Horace, Brussels – 1840 *Noback & Noback (2 volumes), Leipzig – 1851 *Bruhns, Leipzig – 1881 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 Picard, 11 ''pouces'' 3.11 ''lignes'' by 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 newly formed German Empire adopted the metric system in 1871. The palm (typically 200 mm to 280 mm) 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).


Obsolete feet details

In the table below, arbitrary cut-off points of 270 mm and 350 mm have been chosen. In Belgium, the words ''pied'' (French) and ''voet'' (Dutch) would have been used interchangeably.


Notes


Present day uses


International ISO-standard and other intermodal shipping containers

International Standards Organisation (ISO)-defined intermodal 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 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 in Twenty-foot Equivalent Units, or TEUs.


Aviation

Everyday global (civilian) air traffic / aviation continues to be controlled in flight levels (flying altitudes) separated by thousands of feet (although typically read out in hundreds - e.g. flight level 330 actually means 33,000 feet, or about 10 kilometres in altitude).


Dimension

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 from
surface area The surface area of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of ...
in ''
square foot The square foot (plural square feet; abbreviated sq. ft, sf, or ft2; also denoted by '2) is an imperial unit and U.S. customary unit (non- SI, non- metric) of area, used mainly in the United States and partially in Canada, the United Kingdom, B ...
''.


See also

* Anthropic units * History of measurement * International System of Units * Korean units of measurement * Mermin's foot * Pous * Systems of measurement


Notes


References

{{DEFAULTSORT:Foot Customary units of measurement in the United States Human-based units of measurement Imperial units Units of length