Definition
A unit of linear measurement equal to forty poles, one-eighth of a mile, or 220 yards (approximately 201 meters). In legal contexts, the furlong appears primarily in property descriptions, boundary disputes, conveyances of land, and statutes governing highway or road dimensions. Though rarely used in modern drafting, it survives in older deeds, surveys, and land grants where distances were expressed in furlongs, chains, poles, and links rather than feet or meters.
Common Language
Modern common usage (Wiktionary): A unit of distance equal to one-eighth of a mile (220 yards, or approximately 201 meters), now mainly used in measuring distances in horse racing. Also, historically, a unit of land area one furlong square (roughly ten acres), and an undefined portion of an unenclosed field.
Historical common usage (Webster's 1913): The eighth part of a mile; forty rods; two hundred and twenty yards.
The legal and common meanings are substantially aligned for the linear definition. The gap that matters for researchers is the area and agrarian usage — the furlong as a strip or block of open-field land — which common dictionaries acknowledge but legal dictionaries ignore entirely. A researcher encountering "furlong" in an early English or colonial instrument describing land rather than distance should not assume the term is used in its linear sense.
Why It Matters in Research
The furlong is an interpretive problem, not a live drafting tool. Researchers encounter it almost exclusively in historical instruments — colonial-era grants, English conveyances, early American deeds, and highway statutes predating metrication or standardized surveying practice.
Several traps exist for the unwary:
First, the furlong's relationship to other historic units must be kept straight. One furlong equals 10 chains (Gunter's chain), 40 poles (also called rods or perches), or 220 yards. Confusion between poles and furlongs — or between the linear furlong and the area furlong (see below) — can produce significant errors in reconstructing boundary lines or lot sizes.
Second, the term "furlong" was not always used with precision in pre-modern sources. In open-field agricultural systems, "furlong" sometimes described an irregular strip of unenclosed land — a subdivision of a common field — rather than a fixed linear distance. This usage does not appear in Black's or Bouvier's but is well documented in English agrarian history and surfaces in early English legal instruments copied into American colonial records.
Third, modern land disputes involving old deeds may require expert surveying testimony to convert furlong-based descriptions into contemporary measurements. Researchers locating cases involving boundary disputes in jurisdictions with large colonial-era land grant histories (Virginia, Pennsylvania, Massachusetts, the Carolinas) should anticipate furlong-based descriptions and plan accordingly.
Fourth, in statutory contexts, English road law and some early American highway statutes defined road widths or distances in furlongs. Locating the applicable version of such a statute — and confirming whether the furlong used was the standard English furlong or a locally variant measure — can matter in historical right-of-way litigation.
The furlong remains current in one narrow context: horse racing, where race distances are still officially expressed in furlongs in the United States and United Kingdom. This usage is unlikely to appear in legal research except in the interpretation of racing regulations or wagering statutes.
Historical Dictionary Support
Black's Law Dictionary and Bouvier's Law Dictionary are in complete agreement: a furlong is forty poles, or one-eighth of a mile. Neither source elaborates further. This brevity is appropriate for legal dictionaries of their era, where the furlong was a standard surveying unit requiring no explanation for working practitioners.
What both sources omit is meaningful for researchers. Neither addresses the agrarian or open-field usage of "furlong" as an area or strip of land, which appears in English legal instruments and was carried into some colonial American documents. Neither flags the unit's relationship to Gunter's chain, the primary surveying instrument of the 17th through 19th centuries, which was calibrated in chains and links with the furlong as a convenient benchmark. And neither notes that local variation in the length of the pole or perch — which historically ranged from 15 to 18 feet in different English localities before standardization at 16.5 feet — could produce a furlong of slightly different absolute length depending on the instrument's date and place of origin.
Researchers relying solely on Black's or Bouvier's for furlong disputes in early instruments should supplement with historical surveying treatises and agrarian history sources.
Jurisdictional Note
The furlong as a unit of measure is largely uniform across common-law jurisdictions in its linear definition. Variation arises historically at the level of local customary measures for the pole or perch from which the furlong was calculated. Researchers working with pre-standardization instruments in English or early American records should verify whether the local pole measure was 16.5 feet (the eventual standard) or a regional variant.