A furlong is a measure of distance within Imperial units and U.S. customary units, and is equal to 660 feet or 201.168 metres. There are eight furlongs in a mile.

Distances for thoroughbred horse races in the United Kingdom, Ireland and the United States are still given in miles and furlongs (example), but the unit is otherwise no longer in common use — and even in that discipline its usage is mostly confined to denoting distances of less than one mile.

Coincidentally, 5 furlongs is approximately 1 kilometre (1.00584 to be exact).

History

The name "furlong" derives from the Old English words furh (furrow) and lang (long). Dating back at least to the ninth century, it originally referred to the length of the furrow in one acre of a ploughed open field (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. For this reason, it was once also called an acre's length.

The furlong was historically viewed as equivalent to the Roman stade (stadium), which in turn derived from the Greek system. 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 (often very symbolic) 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. A league was considered to be the distance a man could walk in one day, and the mile consisted of 1000 passus (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, rod, furlong, and mile. The rod was 5 1/2 yards (16 1/2 feet), and the mile was eight furlongs, so the definition of the furlong became 40 rods and that of the mile 5280. (In other words, the reason the prime number 11 slipped into the English and subsequently the British and US systems was to accomodate the rod.)

The official use of furlong was abolished in the United Kingdom under the Weights and Measures Act 1985, which also abolished from official use many other traditional units of measurement.

Trivia

• 0.0001663095 metre per second or roughly one centimetre per minute (in SI units)
• 0.001995714 inches per second (in Imperial units)

• a car travelling at 60 km/h (37 mph) is travelling at a speed of 100,214.7 furlongs per fortnight;
• a Boeing 737 cruising at 420 knots or 216.2 m/s (i.e. typical 0.8 Mach cruise) is travelling at 1,300,013.7 furlongs per fortnight;
• the speed of light in vacuum is approximately 1.803 furlongs per fortnight;
• one furlong per fortnight is 0.166 millimetres per second, which would be barely noticeable to the naked eye (the tip of an hour hand on a clock, measuring 3.75 feet in length, travels at about 1 furlong per fortnight).

The city of Chicago's street numbering system allots a measure of 800 address units to each mile. Logically, streets were subsequently laid out 8 to the mile. This means that every block in a typical Chicago neighborhood (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. However, the blocks are irregular in shape as one moves further out from the center, but the numbering system remains the same (800 units to each mile) everywhere in Salt Lake County.

Units of length | Imperial units | Customary units in the United States

Furlong | Furlong | Furlong | Furlong | Furlong | ハロン (単位) | Furlong | Фурлонг | Furlong | Furlong | 浪 (量度單位)