foot | |
---|---|
Unit system | Imperial/US units |
Unit of | Length |
Symbol | ft or ′ |
Conversions | |
1 ft in ... | ... is equal to ... |
Imperial/US units | 1/3 yd 12 in |
Metric (SI) units | 0.3048 m 30.48 cm |
The foot (pl. feet), standard symbol: ft, [1] [2] 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. 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, 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 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 country that uses the international foot in preference to the meter in its commercial, engineering, and standards activities. [3] 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. [4] [5] The foot is recognized as an alternative expression of length in Canada, [6] officially defined as a unit derived from the meter [7] although both the UK and Canada have partially metricated 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.
The length of the international foot corresponds to a human foot with shoe size of 13 (UK), 14 (US male), 15.5 (US female) or 48 (EU sizing).
Historically, the human body has been used to provide the basis for units of length. [8] The foot of an adult Caucasian male is typically about 15.3% of his height, [9] 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 of Egypt, India, and Mesopotamia preferred the cubit, while the people of Rome, Greece, and China 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). [10] 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 30 cm (11.8 in).
The Greek foot (πούς, pous) had a length of 1/600 of a stadion, [11] one stadion being about 181.2 m (594 ft); [12] therefore a foot was, at the time, 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); the former was close to the size of the Roman foot.
The standard Roman foot (pes) was normally about 295.7 mm (11.6 in) (97% of today's measurement), [13] but, in the provinces, the so-called pes Drusianus (foot of Nero Claudius Drusus) was used, with a length of about 334 mm (13.1 in). (In reality, this foot predated Drusus.) [14]
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 AD 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. [15] The toise has 6 pieds (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 of Charlieu 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) [Note 1] was used. At the same time, monastic buildings used the Carolingian foot of 340 mm (13.4 in). [Note 1] [16]
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: [17] [18]
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 lawful rood to measure and survey the land with, and the 16th part of it shall be the right and lawful foot.
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 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. [19]
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 335 mm (13.2 in) was introduced to England either by the Belgic Celts during their invasions prior to the Romans or by the Anglo-Saxons 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. Henry I was said to have ordered a new standard to be based upon the length of his own arm and, by the c. 1300 Act concerning the Composition of Yards and Perches [20] traditionally credited to Edward I or II, the statute foot was a different measure, exactly 10/11 of the old (Belgic) foot. The barleycorn, inch, ell, and yard were likewise shrunk, while rods and furlongs remained the same. [21] 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.
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. [22]
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.
The IEEE standard symbol for a foot is "ft". [1] In some cases, the foot is denoted by a prime, often approximated by an apostrophe, and the inch by a double prime; for example, 2 feet 4 inches is sometimes denoted as 2′ 4″. [23]
In Imperial units, the foot was defined as 1/3 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. [24] 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 0.9143969 m, [25] implying a pre-1959 UK foot of 0.3047990 m.
The UK adopted the international yard for all purposes through the Weights and Measures Act 1963, effective January 1, 1964. [26]
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 the state 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 denoted survey feet to distinguish them from the international foot. The United Kingdom was unaffected by this problem, as the retriangulation 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 the Mendenhall Order of 1893 as 39.37 inches = 1 m (making a US foot exactly 1200/3937 meters, approximately 0.30480061 m). [27] [28] 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. [29]
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, and the United States Department of Commerce are phasing out the US survey foot beginning in 2023. [30] [31] [27] However, its relevance may persist, as the Federal Register Notice says: [32]
The Indian survey foot is defined as exactly 0.3047996 m, [33] 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, [34] which is also used by the Global Positioning System.
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.
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. [36]
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: [37]
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 (10.78 in) while the piede in Venice was 347.73 millimeters (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, 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. [45]
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 [46] and the newly formed German Empire adopted the metric system in 1871. [47]
The palm (typically 200 mm to 280 mm) 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 ]
In the table below, arbitrary cut-off points of 270 mm and 350 mm have been chosen.[ citation needed ]
Location | Modern country | Local name | Metric equivalent (mm) | Comments |
---|---|---|---|---|
Vienna | Austria | Wiener Fuß | 316.102 [44] [48] | |
Tyrol | Austria | Fuß | 334.12 [37] | |
Ypres (Ieper) | Belgium | voet | 273.8 [49] | |
Bruges/Brugge | Belgium | voet | 274.3 [49] | |
Brussels | Belgium | voet | 275.75 [49] | |
Hainaut | Belgium | pied | 293.39 [41] | |
Liège | Belgium | pied | 294.70 [41] | |
Kortrijk | Belgium | voet | 297.6 [49] | |
Aalst | Belgium | voet | 277.2 [49] | |
Mechelen | Belgium | voet | 278.0 [49] | |
Leuven | Belgium | voet | 285.5 [49] | |
Tournai | Belgium | pied | 297.77 [41] | |
Antwerp | Belgium | voet | 286.8 [49] | |
China | China | tradesman's foot | 338.3 [50] | |
China | China | mathematician's foot | 333.2 [50] | |
China | China | builder's foot | 322.8 [50] | |
China | China | surveyor's foot | 319.5 [50] | |
Moravia | Czech Republic | stopa | 295.95 [37] | |
Prague | Czech Republic | stopa | 296.4 [43] | (1851) Bohemian foot or shoe |
301.7 [38] | (1759) Quoted as "11 pouces1+3/4lignes" [Notes 1] | |||
Denmark | Denmark | Fod | 313.85 [44] | Until 1835, thereafter the Prussian foot |
330.5 [38] | (1759) Quoted as "2+1/2lignes larger than the pied [of Paris]" [Notes 1] | |||
France | France | pied du roi | 324.84 [51] | [Notes 2] |
Angoulême | France | pied d'Angoulême | 347.008 [52] | |
Bordeaux (urban) | France | pied de ville de Bordeaux | 343.606 [52] | |
Bordeaux (rural) | France | pied de terre de Bordeaux | 357.214 [52] | |
Strasbourg | France | pied de Strasbourg | 294.95 [52] | |
Württemberg | Germany | Fuß | 286.49 [37] | |
Hanover | Germany | Fuß | 292.10 [37] | |
Augsburg | Germany | Römischer Fuß | 296.17 [42] | |
Nuremberg | Germany | Fuß | 303.75 [42] | |
Meiningen-Hildburghausen | Germany | Fuß | 303.95 [37] | |
Oldenburg | Germany | Römischer Fuß | 296.41 [37] | |
Weimar | Germany | Fuß | 281.98 [37] | |
Lübeck | Germany | Fuß | 287.62 [44] | |
Aschaffenburg | Germany | Fuß | 287.5 [41] | |
Darmstadt | Germany | Fuß | 287.6 [41] | Until 1818, thereafter the Hessen "metric foot" |
Bremen | Germany | Fuß | 289.35 [44] | |
Rhineland | Germany | Fuß | 313.7 [50] | |
Berlin | Germany | Fuß | 309.6 [50] | |
Hamburg | Germany | Fuß | 286.8 [50] | |
Bavaria | Germany | Fuß | 291.86 [37] | |
Aachen | Germany | Fuß | 282.1 [42] | |
Leipzig | Germany | Fuß | 282.67 [37] | |
Dresden | Germany | Fuß | 283.11 [37] | |
Saxony | Germany | Fuß | 283.19 [44] | |
Prussia | Germany, Poland, Russia etc. | Rheinfuß | 313.85 [44] | |
Frankfurt am Main | Germany | Fuß | 284.61 [37] | |
Venice & Lombardy | Italy | 347.73 [37] | ||
Turin | Italy | 323.1 [50] | ||
Rome | Italy | piede romano | 297.896 [52] | |
Riga | Latvia | pēda | 274.1 [50] | |
Malta | Malta | pied | 283.7 [50] | |
Utrecht | Netherlands | voet | 272.8 [50] | |
Amsterdam | Netherlands | voet | 283.133 [40] | Divided into 11 duimen (inches) |
Honsbossche en Rijpse | Netherlands | voet | 285.0 [40] | |
’s Hertogenbosch | Netherlands | voet | 287.0 [40] | |
Gelderland | Netherlands | voet | 292.0 [40] | |
Bloois (Zeeland) | Netherlands | voet | 301.0 [40] | |
Schouw | Netherlands | voet | 311.0 [40] | |
Rotterdam | Netherlands | voet | 312.43 [41] | |
Rijnland | Netherlands | voet | 314.858 [40] | |
Norway | Norway | fot | 313.75 [53] | (1824–1835) [Notes 3] Thereafter as for Sweden. |
Warsaw | Poland | stopa | 297.8 [54] | Until 1819 |
288.0 [41] | (From 1819) Polish stopa | |||
Lisbon | Portugal | Pé | 330.0 [42] | (From 1835) [Notes 4] |
South Africa | South Africa | Cape foot | 314.858 [55] | Originally equal to the Rijnland foot; redefined as 1.033 English feet in 1859. |
Burgos and Castile | Spain | Pie de Burgos/ Castellano | 278.6 [38] | (1759) Quoted as "122.43 lignes" [Notes 1] |
Toledo | Spain | Pie | 279.0 [38] | (1759) Quoted as "10 pouces 3.7 lignes" [Notes 1] |
Sweden | Sweden | fot | 296.9 [44] | = 12 tum (inches). The Swedish fot was also used in Finland ("jalka"). |
Zürich | Switzerland | 300.0 [50] | ||
Galicia | Ukraine, Poland | stopa galicyjska | 296.96 [41] | Part of Austria before World War I |
Scotland | United Kingdom | fuit, fit, troigh | 305.287 [56] | [Notes 5] |
In Belgium, the words pied (French) and voet (Dutch) would have been used interchangeably.[ citation needed ]
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.
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).
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 in square foot . [57]
The acre is a unit of land area used in the imperial and US customary systems. It is traditionally defined as the area of one chain by one furlong, which is exactly equal to 10 square chains, 1⁄640 of a square mile, 4,840 square yards, or 43,560 square feet, and approximately 4,047 m2, or about 40% of a hectare. Based upon the international yard and pound agreement of 1959, an acre may be declared as exactly 4,046.8564224 square metres. The acre is sometimes abbreviated ac but is usually spelled out as the word "acre".
A furlong is a measure of distance in imperial units and United States customary units equal to one eighth of a mile, equivalent to any of 660 feet, 220 yards, 40 rods, 10 chains or approximately 201 metres. It is now mostly confined to use in horse racing, where in many countries it is the standard measurement of race lengths, and agriculture, where it is used to measure rural field lengths and distances.
The inch is a unit of length in the British imperial and the United States customary systems of measurement. It is equal to 1/36 yard or 1/12 of a foot. Derived from the Roman uncia ("twelfth"), the word inch is also sometimes used to translate similar units in other measurement systems, usually understood as deriving from the width of the human thumb.
The imperial system of units, imperial system or imperial units is the system of units first defined in the British Weights and Measures Act 1824 and continued to be developed through a series of Weights and Measures Acts and amendments.
The metre is the base unit of length in the International System of Units (SI).
The mile, sometimes the international mile or statute mile to distinguish it from other miles, is a British imperial unit and United States customary unit of distance; both are based on the older English unit of length equal to 5,280 English feet, or 1,760 yards. The statute mile was standardised between the British Commonwealth and the United States by an international agreement in 1959, when it was formally redefined with respect to SI units as exactly 1,609.344 metres.
Metrication or metrification is the act or process of converting to the metric system of measurement. All over the world, countries have transitioned from local and traditional units of measurement to the metric system. This process began in France during the 1790s, and is still continuing more than 200 years later, with the modern International System of Units, as the metric system has not yet been fully adopted in all countries and areas.
United States customary units form a system of measurement units commonly used in the United States and most U.S. territories, since being standardized and adopted in 1832. The United States customary system developed from English units that were in use in the British Empire before the U.S. became an independent country. The United Kingdom's system of measures was overhauled in 1824 to create the imperial system, which was officially adopted in 1826, changing the definitions of some of its units. Consequently, while many U.S. units are essentially similar to their imperial counterparts, there are significant differences between the systems.
The yard is an English unit of length in both the British imperial and US customary systems of measurement equalling 3 feet or 36 inches. Since 1959 it has been by international agreement standardized as exactly 0.9144 meter. A distance of 1,760 yards is equal to 1 mile.
A unit of length refers to any arbitrarily chosen and accepted reference standard for measurement of length. The most common units in modern use are the metric units, used in every country globally. In the United States the U.S. customary units are also in use. British Imperial units are still used for some purposes in the United Kingdom and some other countries. The metric system is sub-divided into SI and non-SI units.
The rod, perch, or pole is a surveyor's tool and unit of length of various historical definitions, often between approximately 3 and 8 meters. In modern US customary units it is defined as 16+1⁄2 US survey feet, equal to exactly 1⁄320 of a mile, or a quarter of a surveyor's chain, and is exactly 5.0292 meters. The rod is useful as a unit of length because integer multiples of it can form one acre of square measure (area). The 'perfect acre' is a rectangular area of 43,560 square feet, bounded by sides 660 feet long and 66 feet wide or, equivalently, 40 rods by 4 rods. An acre is therefore 160 square rods or 10 square chains.
Metrication is the process of introducing the International System of Units, also known as SI units or the metric system, to replace a jurisdiction's traditional measuring units. U.S. customary units have been defined in terms of metric units since the 19th century, and the SI has been the "preferred system of weights and measures for United States trade and commerce" since 1975 according to United States law. However, conversion was not mandatory and many industries chose not to convert, and U.S. customary units remain in common use in many industries as well as in governmental use. Unlike other countries, there is no governmental or major social desire to implement further metrication.
A system of measurement is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce. Systems of measurement in use include the International System of Units or SI, the British imperial system, and the United States customary system.
The following systems arose from earlier systems, and in many cases utilise parts of much older systems. For the most part they were used to varying degrees in the Middle Ages and surrounding time periods. Some of these systems found their way into later systems, such as the Imperial system and even SI.
The link, sometimes called a Gunter’s link, is a unit of length formerly used in many English-speaking countries. In US customary units modern definition, the link is exactly 66⁄100 of a US survey foot, or exactly 7.92 inches or approximately 20.12 cm.
France has a unique history of units of measurement due to its radical decision to invent and adopt the metric system after the French Revolution.
Both the British imperial measurement system and United States customary systems of measurement derive from earlier English unit systems used prior to 1824, that were the result of a combination of the local Anglo-Saxon units inherited from Germanic tribes and Roman units.
The history of the metre starts with the Scientific Revolution that is considered to have begun with Nicolaus Copernicus's publication of De revolutionibus orbium coelestium in 1543. Increasingly accurate measurements were required, and scientists looked for measures that were universal and could be based on natural phenomena rather than royal decree or physical prototypes. Rather than the various complex systems of subdivision then in use, they also preferred a decimal system to ease their calculations.
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. The agreement defined the yard as exactly 0.9144 meters and the avoirdupois pound as exactly 0.45359237 kilograms.
The imperial and US customary measurement systems are both derived from an earlier English system of measurement which in turn can be traced back to Ancient Roman units of measurement, and Carolingian and Saxon units of measure.
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