The rod, perch, or pole (sometimes also lug) is a surveyor's tool and a unit of length with various historical definitions. In British imperial and US customary units, it is defined as feet, equal to exactly of a mile, or yards (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 (a furlong) long and 66 feet (a chain) wide (220 yards by 22 yards) or, equivalently, 40 rods by 4 rods. An acre is therefore 160 square rods or 10 square chains.
The name perch derives from the Ancient Roman unit, the pertica. The measure also has a relationship with the military pike of about the same size. Both measures date from the sixteenth century, when the pike was still utilized in national armies.
The tool has been supplanted, first by steel tapes and later by electronic tools such as surveyor lasers and optical target devices for surveying lands. In dialectal English, the term lug has also been used, although the Oxford English Dictionary states that this unit, while usually of feet, may also be of 15, 18, 20, or 21 feet.
History
In England, the perch was officially discouraged in favour of the rod as early as the 15th century;Encyclopædia Britannica, English measure however, local customs maintained its use. In the 13th century, perches were variously recorded in lengths of , , and ; and even as late as 1820, a House of Commons report notes lengths of , , , , and even . In Ireland, a perch was standardized at , making an Irish chain, furlong and mile proportionately longer by 27.27% than the "standard" English measure.
Until English King Henry VIII seized the lands of the Roman Catholic Church in 1536, modern land measures were essentially unknown. Instead a narrative system of landmarks and lists was used. Henry wanted to raise even more funds for his wars than he had seized directly from church property (he had also assumed the debts of the monasteries), and as James Burke writes and quotes in the book Connections that the English monk Richard Benese "produced a book on how to survey land using the simple tools of the time, a rod with cord carrying knots at certain intervals, waxed and resined against wet weather." Benese described the measure of an acre in terms of a perch:Connections, pbk. p.263
The practice of using surveyor's chains, and perch-length rods made into a detachable stiff chain, came about a century later when iron was a more plentiful and common material. A chain is a larger unit of length measuring , or 22 yards, or 100 links, or 4 rods (20.1168 meters). There are 10 chains or 40 rods in a furlong (eighth-mile), and so 80 chains or 320 rods in one statute mile (1760 yards, 1609.344 m, 1.609344 km); the definition of which was legally set in 1593 and popularized by Royal surveyor (called the 'sworn viewer'"Connections", pbk. p.265) John Ogilby only after the Great Fire of London (1666).
An acre is defined as the area of 10 square chains (that is, an area of one chain by one furlong), and derives from the shapes of new-tech plowsConnections, pbk. p.63 and the desire to quickly survey seized church lands into a quantity of squares for quick sales by Henry VIII's agents; buyers simply wanted to know what they were buying whereas Henry was raising cash for wars against Scotland and France. Consequently, the surveyor's chain and surveyor rods or poles (the perch) have been used for several centuries in Britain and in many other countries influenced by British practices such as North America and Australia. By the time of the industrial revolution, and with surveys for land sales, canals and railways increasing, surveyor rods such as those used by George Washington were generally made of dimensionally stable metal—semi-flexible drawn wrought iron linkable bar stock (not steel) so the four folded elements of a chain were easily transportable through brush and branches when carried by a single man of a surveyor's crew. With a direct ratio to the length of a surveyor's chain and the sides of both an acre and a square (mile), they were common tools used by surveyors, if only to lay out a known plottable baseline in rough terrain thereafter serving as the reference line for instrumental (theodolite) triangulations.
The rod as a survey measure was standardized by Edmund Gunter in England in 1607 as a quarter of a chain (of ), or long.
In ancient cultures The perch (pertica) as a lineal measure in Rome (also decempeda) was 10 Roman feet (2.96 metres), and in France varied from 10 feet (perche romanie) to 22 feet (perche d'arpent—apparently of "the range of an arrow"—about ). To confuse matters further, by ancient Roman definition, an arpent equalled 120 Roman feet. The related unit of square measure was the scrupulum or decempeda quadrata, equivalent to about .
In continental Europe
Units comparable to the perch, pole or rod were used in many European countries, with names that include and canne, , and pertica, and . They were subdivided in many different ways, and were of many different lengths.
+Rods and similar units in continental EuropePlaceLocal nameLocal equivalentMetric equivalent (meters) Aachen Feldmeßruthe 16 Fuß4.512 Amsterdam Roede 13 Voet3.681 Aubenas, Ardèche canne 8 pans1.985 Baden, Grand Duchy of Ruthe 10 Fuß3.0 Basel, Canton of Ruthe 16 Fuß4.864 Bern, Canton of Ruthe 10 Fuß2.932 Barcelona canna 8 palmos1.581 Braunschweig Ruthe 16 Fuß4.565 Bremen Ruthe 8 Ellen or 16 Fuß4.626 Brussels Ruthe 20 Fuß4.654 Cagliari, Sardinia canna 10 palmi2.322 Calenberg Land Ruthe 16 Fuß4.677 Cassel, Hessen Ruthe 14 Fuß4.026 Denmark Ruthe 10 Fuß3.138 Ruthe 8 Fuß2.598 Hamburg Geestruthe 16 Fuß4.583 Hamburg Marschruthe 14 Fuß4.010 Hannover Ruthe 16 Fuß4.671 France Perche 3 toises5.847 France Perche (for woodland) toises7.145 Genoa canna 10 palmi2.5 Jever, Oldenburg Ruthe 20 Fuß4.377 Mallorca canna 8 palmos1.714 Malta canna 8 palmi2.08 Mecklenburg Ruthe 16 Fuß4.655 Menorca, but not Mahón canna1.599 Menorca, city of Mahon canna 8 palmos1.714 Messina, Sicily canna 8 palmi2.113 Montauban, Tarn-et-Garonne canne 8 pans1.783 Morocco canna 8 palmos1.714 Naples canna (for cloth) 8 palmi Naples, Kingdom of: Apulia, Calabria, Eboli, Foggia, Lucera percha 7 palmi1.838 Naples, Kingdom of: Capua percha palmi1.892 Naples, Kingdom of: Fiano, Naples percha palmi2.014 Naples, Kingdom of: Caggiano, Cava, Nocera, Rocce, Salerno percha palmi1.971 Nuremberg, Bavaria Ruthe 16 Fuß4.861 Oldenburg Ruthe 20 Fuß5.927 Palermo, Sicily canna 8 palmi1.942 Parma Pertica 6 bracci3.25 Poland Pręt łokci or 10 pręcików4.320 Prussia, Rheinland Ruthe 12 Fuß3.766 Rijnland Roede 12 Voet3.767 Rome canna (for cloth)2 Rome canna (for building)2.234 Saragoza canna2.043 Saxony Ruthe 16 Leipziger Fuß4.512 Sweden Ruthe 16 Fuß4.748 Tortosa canna1.7 Tuscany, Grand-Duchy of (Florence, Pisa) canna 5 bracci2.918 Uzès, Gard canne 8 pans1.98 Waadt, Canton of Ruthe or toise courante 10 Fuß3 Württemberg Reichsruthe 10 Fuß2.865 Württemberg old Ruthe 16 Fuß4.583 Venice, Republic of Pertica 6 piedi2.084 Zürich, Canton of Ruthe 10 Fuß3.009
In Britain and Ireland
In England, the rod or perch was first defined in law by the Composition of Yards and Perches, one of the statutes of uncertain date from the late 13th to early 14th centuries: tres pedes faciunt ulnam, quinque ulne & dimidia faciunt perticam (three feet make a yard, five and a half yards make a perch).
The length of the chain was standardized in 1620 by Edmund Gunter at exactly four rods. Fields were measured in acres, which were one chain (four rods) by one furlong (in the United Kingdom, ten chains).
Bars of metal one rod long were used as standards of length when surveying land. The rod was still in use as a common unit of measurement in the mid-19th century, when Henry David Thoreau used it frequently when describing distances in his work, Walden.
In traditional Scottish units, a Scottish rood (ruid in Lowland Scots, ròd in Scottish Gaelic), also fall measures 222 inches (6 ells).
Modern use and definition The rod was phased out as a legal unit of measurement in the United Kingdom as part of a ten-year metrication process that began on 24 May 1965. In the UK and elsewhere, some vestigial use of the term persists. For example, sizes of allotment gardens continue to be measured in square poles in some areas, sometimes being referred to simply as poles rather than square poles.
Despite no longer being in widespread use, the rod is still employed in certain specialized fields. In recreational canoeing, maps measure portages (overland paths where canoes must be carried) in rods; typical canoes are approximately one rod long. The term is also in widespread use in the acquisition of pipeline easements, as the offers for an easement are often expressed on a "price per rod".
In Vermont, the default right-of-way width of state and town highways and trails is three rods (49 ft 6 in, 15.09 m). Rods can also be found on the older legal descriptions of tracts of land in the United States, following the "metes and bounds" method of land survey; as shown in this actual legal description of rural real estate:In the United States, the rod, along with the chain, furlong, and statute mile (as well as the survey inch and survey foot) were based on the pre-1959 values for United States customary units of linear measurement until 1 January 2023. The Mendenhall Order of 1893 defined the yard as exactly meters, with all other units of linear measurement, including the rod, based on the yard. In 1959, an international agreement (the international yard and pound agreement), defined the yard as the fundamental unit of length in the Imperial/USCU system, defined as exactly 0.9144 metres. However, the above-noted units, when used in historical surveying, may retain their pre-1959 values, depending on the legislation in each state; the terms are not used in modern surveying (see below) and if they were to be used they would have the values by reference to the international foot.
The U.S. National Geodetic Survey and National Institute of Standards and Technology have recently replaced the definition for the above-mentioned units by the international 1959 definition of the foot, being exactly 0.3048 meters. In the United States until 1 January 2023, the rod was defined in terms of 'survey' feet: it was 16.5 US survey feet which equalled approximately 5.029 210 058 meters; since 1 January 2023 survey feet have been deprecated and the rod formally is defined as exactly 16.5 feet (international feet) or exactly 5.0292 meters.
Area and volume The terms pole, perch, rod and rood have been used as units of area, and perch is also used as a unit of volume. As a unit of area, a square perch (the perch being standardized to equal feet, or yards) is equal to a square rod, or acre. There are 40 square perches to a rood (for example a rectangular area of 40 rods times one rod), and 160 square perches to an acre (for example a rectangular area of 40 rods times 4 rods). This unit is usually referred to as a perch or pole even though square perch and square pole were the more precise terms. Rod was also sometimes used as a unit of area to refer to a rood.
However, in the traditional French-based system in some countries, 1 square perche is 42.21 square metres.
As of August 2013, perches and roods are used as government survey units in Jamaica. They appear on most property title documents. The perch is also in extensive use in Sri Lanka, being favored even over the rood and acre in real estate listings there. Perches were informally used as a measure in Queensland real estate until the early 21st century, mostly for historical gazetted properties in older suburbs.
Volume