Furlong

# Furlong

Discussion

Encyclopedia
A furlong is a measure of distance
Distance
Distance is a numerical description of how far apart objects are. In physics or everyday discussion, distance may refer to a physical length, or an estimation based on other criteria . In mathematics, a distance function or metric is a generalization of the concept of physical distance...

in imperial unit
Imperial unit
The system of imperial units or the imperial system is the system of units first defined in the British Weights and Measures Act of 1824, which was later refined and reduced. The system came into official use across the British Empire...

s and U.S. customary units equal to one-eighth of a mile
Mile
A mile is a unit of length, most commonly 5,280 feet . The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical mile...

, equivalent to 220 yard
Yard
A yard is a unit of length in several different systems including English units, Imperial units and United States customary units. It is equal to 3 feet or 36 inches...

s, 660 feet, 40 rod
Rod (unit)
The rod is a unit of length equal to 5.5 yards, 5.0292 metres, 16.5 feet, or of a statute mile. A rod is the same length as a perch or a pole. In old English, the term lug is also used.-History:...

s, or 10 chains
Gunter's chain
Gunter's chain is a measuring device used for land survey. It was designed and introduced in 1620 by English clergyman and mathematician Edmund Gunter long before the development of the theodolite and other more sophisticated equipment, enabling plots of land to be accurately surveyed and plotted,...

. The exact value of the furlong varies slightly among English-speaking countries.

Five furlongs are approximately 1 kilometre
Kilometre
The kilometre is a unit of length in the metric system, equal to one thousand metres and is therefore exactly equal to the distance travelled by light in free space in of a second...

(1.0058 km is a closer approximation). Since the original definition of the metre
Metre
The metre , symbol m, is the base unit of length in the International System of Units . Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole , its definition has been periodically refined to reflect growing knowledge of metrology...

was one-quarter of one ten-millionth of the circumference of the Earth (along the great circle coincident with the meridian
Meridian (geography)
A meridian is an imaginary line on the Earth's surface from the North Pole to the South Pole that connects all locations along it with a given longitude. The position of a point along the meridian is given by its latitude. Each meridian is perpendicular to all circles of latitude...

of longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....

passing through Paris), the circumference of the Earth is about 40,000 km or about 200,000 furlongs.

## History

The name furlong derives from the Old English
Old English language
Old English or Anglo-Saxon is an early form of the English language that was spoken and written by the Anglo-Saxons and their descendants in parts of what are now England and southeastern Scotland between at least the mid-5th century and the mid-12th century...

words (furrow) and (long). Dating back at least to early Anglo-Saxon times, it originally referred to the length of the furrow in one acre
Acre
The acre is a unit of area in a number of different systems, including the imperial and U.S. customary systems. The most commonly used acres today are the international acre and, in the United States, the survey acre. The most common use of the acre is to measure tracts of land.The acre is related...

of a ploughed open field
Open field system
The open field system was the prevalent agricultural system in much of Europe from the Middle Ages to as recently as the 20th century in some places, particularly Russia and Iran. Under this system, each manor or village had several very large fields, farmed in strips by individual families...

(a medieval communal field which was divided into strips). The system of long furrows arose because turning a team of oxen pulling a heavy plough was difficult. This offset the drainage advantages of short furrows and meant furrows were made as long as possible. An acre
Acre
The acre is a unit of area in a number of different systems, including the imperial and U.S. customary systems. The most commonly used acres today are the international acre and, in the United States, the survey acre. The most common use of the acre is to measure tracts of land.The acre is related...

is an area that is one furlong long and one chain (66 feet or 22 yards) wide. For this reason, the furlong was once also called an acre's length, though of course in modern usage an area of one acre
Acre
The acre is a unit of area in a number of different systems, including the imperial and U.S. customary systems. The most commonly used acres today are the international acre and, in the United States, the survey acre. The most common use of the acre is to measure tracts of land.The acre is related...

can be any shape.

Among the early Saxons, the rod was the fundamental unit of land measurement. A furlong was ten rods, an acre 4 × 40 rods, or 4 rods by 1 furlong. and thus 160 square rods. At the time, the Saxons used the North German foot, which was 10% longer than the foot of today. When England switched to the shorter foot in the late 13th century, rods and furlongs remained unchanged, since property boundaries were already defined in rods and furlongs. The only thing that changed was the number of feet and yards in a rod or a furlong, and the number of square feet and square yards in an acre. The definition of the rod went from 15 old feet to 16 1/2 new feet, or from 5 old yards to 5 1/2 new yards. The furlong went from 600 old feet to 660 new feet, or from 200 old yards to 220 new yards. The acre went from 36,000 old square feet to 43,560 new square feet, or from 4000 old square yards to 4840 new square yards.

The furlong was historically viewed as equivalent to the Roman stade (stadium)
Ancient Roman units of measurement
The ancient Roman units of measurement were built on the Hellenic system with Egyptian, Hebrew, and Mesopotamian influences. The Roman units were comparatively consistent and well documented.-Length:Notes...

, which in turn derived from the Greek system
Ancient Greek units of measurement
Ancient Greek units of measurement would later create the foundation of Egyptian, and formed the basis of the later Roman system.Generally speaking, standards of measurement within the ancient Greek world varied according to location and epoch. Systems of ancient weights and measures evolved as...

. For example the King James Bible will use the term "furlong" in place of the Greek "stadion", whereas modern translations will translate into miles in the main text and relate the original numbers in footnotes.

In the Roman system, there were 625 feet to the stade, eight stade to the mile, and three miles to the league
League (unit)
A league is a unit of length . It was long common in Europe and Latin America, but it is no longer an official unit in any nation. The league originally referred to the distance a person or a horse could walk in an hour...

. A league was considered to be the distance a man could walk in one hour, and the mile (mille, meaning one thousand) consisted of 1000 passus (paces, 5 feet, or double-step).

After the fall of Rome, Medieval Europe continued with the Roman system, which proceeded to "diversify" leading to serious complications in trade, taxation, etc. Around the turn of the century of 1300, England by decree standardized a long list of measures. Among the important units of distance and length at the time were foot, yard
Yard
A yard is a unit of length in several different systems including English units, Imperial units and United States customary units. It is equal to 3 feet or 36 inches...

, rod
Rod (unit)
The rod is a unit of length equal to 5.5 yards, 5.0292 metres, 16.5 feet, or of a statute mile. A rod is the same length as a perch or a pole. In old English, the term lug is also used.-History:...

(or pole), furlong, and mile
Mile
A mile is a unit of length, most commonly 5,280 feet . The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical mile...

. The rod was 5½ yards or 16½ feet (= 3 feet/yard × 5½ yards), and the mile was 8 furlongs, so the definition of the furlong became 40 rods and that of the mile became 5280 feet (= 8 furlongs × 40 rods/furlong × 16½ feet/rod).

A 1675 description states, "Dimensurator or Measuring Instrument whereof the mosts usual has been the Chain, and the common length for English Measures 4 Poles, as answering indifferently to the Englishs Mile and Acre, 10 such Chains in length making a Furlong, and 10 single square Chains an Acre, so that a square Mile contains 640 square Acres." ---John Ogilby, Britannia, 1675

The official use of furlong was abolished in the United Kingdom under the Weights and Measures Act
Weights and Measures Act
A Weights and Measures Act is an Act of Parliament determining trade law where the weight or size of the goods being traded are important. For example, if a bottle of milk is for sale and has a label saying it contains one pint, then the law states that it must contain that amount.-United...

of 1985, which also abolished from official use many other traditional units of measurement.

## Use

Today the unit enjoys very limited use, with the notable exception of horse racing
Horse racing
Horse racing is an equestrian sport that has a long history. Archaeological records indicate that horse racing occurred in ancient Babylon, Syria, and Egypt. Both chariot and mounted horse racing were events in the ancient Greek Olympics by 648 BC...

. Distances for thoroughbred horse races in Australia were metricated in 1972 but in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

, Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, and the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, races are still given in miles and furlongs.

The city of Chicago's street numbering system allots a measure of 800 address units to each mile, in keeping with the city's system of eight blocks per mile. This means that every block in a typical Chicago neighbourhood (in either North/South or East/West direction but rarely both) is approximately one furlong in length. Salt Lake City's blocks are also each a square furlong in the downtown area. The blocks become less regular in shape, further out from the centre, but the numbering system (800 units to each mile) remains the same everywhere in Salt Lake County. Bus stops in Ann Arbor, Michigan
Ann Arbor, Michigan
Ann Arbor is a city in the U.S. state of Michigan and the county seat of Washtenaw County. The 2010 census places the population at 113,934, making it the sixth largest city in Michigan. The Ann Arbor Metropolitan Statistical Area had a population of 344,791 as of 2010...

, are about a furlong apart. Blocks in central Logan, Utah
Logan, Utah
-Layout of the City:Logan's city grid originates from its Main and Center Street block, with Main Street running north and south, and Center east and west. Each block north, east, south, or west of the origin accumulates in additions of 100 , though some streets have non-numeric names...

, and in large sections of Phoenix, Arizona, are similarly a square furlong in extent (eight to a mile, which explains the series of freeway exits: 19th Ave, 27th, 35th, 43rd, 51st, 59th ...). City blocks in Melbourne
Melbourne
Melbourne is the capital and most populous city in the state of Victoria, and the second most populous city in Australia. The Melbourne City Centre is the hub of the greater metropolitan area and the Census statistical division—of which "Melbourne" is the common name. As of June 2009, the greater...

's Hoddle Grid
Hoddle Grid
The Hoddle Grid is the layout of the streets in the centre of the central business district of Melbourne. Named after its designer, Robert Hoddle, the Grid was laid out in 1837, and later extended...

are also one furlong in length.

The furlong is also a base unit of the obscure FFF system
FFF System
The Furlong/Firkin/Fortnight system is a set of units that uses impractical measurements not seriously deemed suitable for scientific or engineering use. The length unit of the system is the furlong, the mass unit is the mass of a firkin of water, and the time unit is the fortnight...

of units.

## Conversion to SI units

The exact conversion of the furlong to SI units varies slightly among English-speaking countries. In Canada
and the United Kingdom,
which define the furlong in terms the international yard of exactly 0.9144 metre, a furlong is 201.168 m.
Australia
does not formally define the furlong, but does define the chain and link in terms of the international yard. In the United States, which defines the furlong, chain, rod, and link in terms of the U.S. survey foot of exactly meter,
a furlong is approximately 201.1684 m; the US does not formally define a "survey yard". The difference of approximately 2 parts per million between the US value and the "international" value is insignificant for most practical measurements.