Foot (unit)

• 1. Introduction

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  The foot, standard symbol ft, is one of the oldest units of measurement still in daily use, yet its history is far stranger than its name suggests. In ancient Rome, the standard pes measured about 295.7 millimeters. In Venice, a foot stretched to 347.73 millimeters. In Ypres, Belgium, a voet stopped at just 273.8 millimeters. The same word, dozens of meanings, and centuries of confusion. How did a unit rooted in the literal human body become the precisely defined international standard of 0.3048 meters? And why does only one industrialized country still prefer it over the metric system? The answers run from Bronze Age Indus cities to a 16th-century German geometry book, from Charlemagne's failed reform to a July 1959 international agreement that finally nailed the foot down to the millimeter.

• 2. Bodies as Rulers

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  The foot of an adult European-American male is typically about 15.3 percent of his height, giving a person of 175 centimeters a foot-length of roughly 268 millimeters. That biological fact is where the story begins. Archaeologists believe that Egypt, India, and Mesopotamia tended toward the cubit, while Rome, Greece, and China favored the foot. The Indus cities of the Bronze Age, operating under Harappan linear measures, used a foot of 13.2 inches and a cubit of 20.8 inches. Egypt had its own equivalent, a measure of four palms or 16 digits called the djeser, reconstructed at about 30 centimeters. The Greek foot, known as the pous, equaled one sixth of a stadion, and since a stadion ran about 181.2 meters, a Greek foot came to roughly 302 millimeters. That said, the exact size shifted from city to city, ranging between 270 and 350 millimeters, though temple builders seem to have favored a narrower band of 295 to 325 millimeters. The Roman standard pes held more tightly at about 295.7 millimeters, but in the province of Germania Inferior, a variant called the pes Drusianus, named for Nero Claudius Drusus yet predating him, ran to about 334 millimeters. Both the Greeks and the Romans originally divided their foot into 16 digits, though the Romans later also divided it into 12 unciae, the root of both the English words inch and ounce.

• 3. Medieval Attempts at Order

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  In 790, Charlemagne attempted to reform the units of measure across his domains, anchoring his lengths to the toise de l'Ecritoire, defined as the distance between the fingertips of a man's outstretched arms. His toise held 6 pieds, each 326.6 millimeters. The effort collapsed in practice. An analysis of Charlieu Abbey shows that in the 9th century the builders there used a Roman foot of 296.1 millimeters, yet when the abbey was rebuilt in the 10th century, a foot of about 320 millimeters appeared in its walls. Monastic buildings of the same era used the Carolingian foot of 340 millimeters. Three different feet, side by side, in a single region within a century of Charlemagne's push for uniformity. England had its own disorder. By around 950, English kings seem to have ordered measures based on an iron yardstick kept first at Winchester and then at London, with uncertain effect. Henry I was said to have set a new standard from the length of his own arm. A c. 1300 act traditionally credited to Edward I or Edward II established the statute foot as a specific fraction of the old Belgic foot, simultaneously shrinking the barleycorn, inch, ell, and yard while leaving rods and furlongs unchanged. The ambiguity over the mile's length persisted until the 1593 Act, which codified the statute mile as comprising 5,280 feet.

• 4. The Stonehenge Connection

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  Archaeologists Mike Parker Pearson and Andrew Chamberlain proposed a unit called the Neolithic long foot, derived from calculations based on surveys of Phase 1 elements at Stonehenge. Their analysis found that the underlying diameters of the stone circles were consistently laid out in multiples of a base unit amounting to 30 long feet, and they calculated that one long foot equaled 1.056 of a modern international foot, or about 12.672 inches (0.3219 meters). The same unit appears in some of the stone lintels at Stonehenge itself and in the diameter of the southern circle at nearby Durrington Walls. Evidence that this unit spread beyond Salisbury Plain comes from the Folkton Drums, Neolithic artifacts carved from chalk and found in Yorkshire, whose circumferences divide exactly as integers into ten long feet. A similar object, the Lavant drum, excavated at Lavant in Sussex, shares the same property. Later, the Belgic or North German foot of 335 millimeters arrived in England either with the Belgic Celts before the Roman conquest of AD 43 or with the Anglo-Saxons in the 5th and 6th centuries. After the Romans withdrew and the Saxons came, the Roman foot survived in the construction trades while the Belgic foot was used for measuring land. Jacob Kobel's posthumously published 16th-century work Geometrei described the verification procedure for the foot: gather 16 men of varied heights at a church door on a Sunday, have them stand with left feet one behind the other, and call the total length a lawful rood, with the 16th part serving as the lawful foot.

• 5. A World of Different Feet

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  Before metric standards swept across Europe, virtually every city kept its own foot. The pied du roi in France measured 324.84 millimeters; in Bordeaux the rural foot, the pied de terre, stretched all the way to 357.214 millimeters. Prussia's Rheinfuss matched Denmark's fod at 313.85 millimeters, and that same measure later became the South African Cape foot, formally redefined in 1859 as 1.033 English feet. China maintained at least four distinct feet simultaneously: the tradesman's foot at 338.3 millimeters, the mathematician's foot at 333.2, the builder's foot at 322.8, and the surveyor's foot at 319.5. European scholars responded to this proliferation with reference books: Palaiseau published conversion lists in Bordeaux in 1816, Noback and Noback filled two volumes published in Leipzig in 1851, and Bruhns added another Leipzig volume in 1881. Even within a single language, measurements diverged: the English foot was quoted as 11 pouces 2.6 lignes by Picard, 11 pouces 3.11 lignes by Maskelyne, and 11 pouces 3 lignes by D'Alembert. Germany's fragmentation was particularly acute; before German unification in 1871, dozens of kingdoms, principalities, and free cities each maintained their own standards. The Netherlands and modern Belgium adopted the metric system in 1817. The German Empire followed suit in 1871. Most of the varied feet in use across Europe simply ceased when those countries metricated.

• 6. The 1959 Agreement and What Came After

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  The international yard and pound agreement of July 1959 settled the matter for most of the English-speaking world. The international yard was fixed at exactly 0.9144 meters, making one foot exactly 0.3048 meters. For the United States, this was 2 parts per million shorter than the previous American definition. For Britain, it was 1.7 parts per million longer than the previous British definition. The groundwork had been laid decades earlier, when the British Standards Institution adopted a scientific standard inch of 25.4 millimeters in 1930. Surveying complicated the transition in both the United States and India. Large bodies of existing survey data had been calculated under the old definitions, and the tiny difference between the old survey foot and the new international foot becomes significant over hundreds of miles of coordinate systems. In the US, this gave rise to the survey foot as a parallel definition that continued in official use for decades. On the 31st of December 2022, the National Institute of Standards and Technology, the National Geodetic Survey, and the United States Department of Commerce officially deprecated the US survey foot. The timing was deliberately synchronized with the modernization of the National Spatial Reference System to minimize disruption. Out of 50 states and six other jurisdictions, 40 had legislated that surveying measures should use the US survey foot, six chose the international foot, and ten left the question unresolved. India defined its survey foot as exactly 0.3047996 meters, and its National Topographic Database now uses the metric WGS-84 datum shared with the Global Positioning System.

• 7. Who Still Uses the Foot

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  The United States stands as the only industrialized country that prefers the international foot over the meter in its commercial, engineering, and standards activities. In the United Kingdom, the foot is legally recognized and road signs must use imperial units, though distances appear in miles or yards rather than feet, and bridge clearances are posted in both meters and feet. British public usage of the foot is widespread as a measure of personal height. Canada recognizes the foot as an alternative expression of length, though both the UK and Canada have partially metricated their systems. One durable holdout in international aviation is the flight level, where altitude is measured in feet even outside the English-speaking world, making it one of the rare contexts where a non-metric country's preference shapes global professional practice. The Institute of Electrical and Electronics Engineers uses ft as the standard symbol for the foot, though the prime symbol, sometimes approximated by an apostrophe, remains in common use, as in the notation 2 prime 4 double prime for 2 feet 4 inches. Napoleon briefly revived traditional French measurements in 1812 through the mesures usuelles system, redefining the pied metrique as one third of a meter; that system lasted until 1837. In southwestern Germany's Confederation of the Rhine, founded in 1806, three separate reformed metric feet appeared at once: 25 centimeters in Hesse, 30 centimeters in Baden, and the French one-third meter in the Palatinate.