A league is a unit of length. It was common in Europe and Latin America, but is no longer an official unit in any nation. The word originally meant the distance a person could walk in an hour.  Since the Middle Ages, many values have been specified in several countries.
The Argentine league (legua) is 5.572 km (3.462 mi) or 6,666 varas: 1 vara is 0.83 m (33 in). 
On land, the league is most commonly defined as three miles, though the length of a mile could vary from place to place and depending on the era. At sea, a league is three nautical miles (3.452 miles; 5.556 kilometres). English usage also included many of the other leagues mentioned below (for example, in discussing the Treaty of Tordesillas).
The French lieue – at different times – existed in several variants: 10,000, 12,000, 13,200 and 14,400 French feet, about 3.25 to 4.68 km (2.02 to 2.91 miles). It was used along with the metric system for a while but is now long discontinued.
Metric lieue was used in France from 1812 to 1840, 1 lieue (metric) = 4000 m (E). 
In Yucatán and other parts of rural Mexico, the league is still commonly used in the original sense of the distance that can be covered on foot in an hour, so that a league along a good road on level ground is a greater distance than a league on a difficult path over rough terrain.
- Légua of 18 to a degree = 6,172.84 meters
- Légua of 20 to a degree (Maritime légua) = 5,555.56 meters
- Légua of 25 to a degree = 4,444.44 meters
As a transitory measure, after Portugal adopted the metric system, the metric légua, of 5.0 km, was used.
In Brazil, the légua is still used occasionally, where it has been described as about 6.6 km.
The legua or Spanish league was originally understood as equivalent to 3 millas (Spanish miles).  This varied depending on local standards for the pie (Spanish foot) and on the precision of measurement, but was officially equivalent to 4,180 meters (2.6 miles) before the legua was abolished by Philip II in 1568. It remains in use in parts of Latin America, where its exact meaning varies.
- Legua nautica (nautical league): Between 1400 and 1600 the Spanish nautical league was equal to four Roman miles of 4,842 feet, making it 19,368 feet (5,903 meters or 3.1876 modern nautical miles). That seems pretty straight forward until one realizes that the accepted number of Spanish nautical leagues to a degree varied between 14 1/6 to 16 2/3 so in actual practice the length of a Spanish nautical league was 25,733 feet (4.235 modern nautical miles) to 21,874 feet (3.600 modern nautical miles) respectively. 
- Legua de por grado (league of the degree): From the 15th century through the early 17th century, the Spanish league of the degree was based on four Arabic miles. Although most contemporary accounts used an Arabic mile of 6,444 feet (1,964 meters), which gave a Spanish league of the degree of 25,776 feet (7,857 meters or 4.242 modern nautical miles) others defined an Arabic mile as just 6,000 feet making a Spanish league of the degree 24,000 feet (or 7,315 meters, almost exactly 3.950 modern nautical miles). 
- Legua geographica or geográfica (geographical league): Starting around 1630 the Spanish geographical league was used as the official nautical measurement and continued so through the 1840s. Its use on Spanish charts did not become mandatory until 1718. It was four millias (miles) in length. From 1630 to 1718 a millia was 5,564 feet (1696 meters), making a geographical league of four millias equal 22,256 feet (6784 m or 3.663 modern nautical miles). But from 1718 through the 1830s the millia was defined as the equivalent of just over 5,210 feet, giving a shorter geographical league of just over 20,842 feet (6,353 m or 3.430 modern nautical miles). 
- Legua marítima (maritime league): From around 1840 through the early 20th century, a Spanish marine league equaled 18,263.52 feet (5,566.72 meters or 3.005 79 modern nautical miles), i.e. about 35 feet (10 meters) longer than our modern maritime league. 
In the early Hispanic settlements of New Mexico, Texas, California, and Colorado, a league was also a unit of area, defined as 25 million square varas or about 4,428.4 acres.  This usage of league is referenced frequently in the Texas Constitution. So defined, a league of land would encompass a square that is one Spanish league on each side.
In U.S. linear measure, one league (Symbol: U.S. st. leag.) is equal to 15,840 feet (or three miles). U.S. nautical league (Symbol: U.S. naut. leag.) is equal to 18,228 feet. 
A comparison of the different lengths for a "league", in different countries and at different times in history, is given in the table below. Miles are also included in this list because of the linkage between the two units.
|Length (m)||Name||Where used||From||To||Definition||Remarks|
|1,482||mille passus, milliarium||Roman Empire||Ancient Roman units of measurement|
|1,609.3426||(statute) mile||Great Britain||1592||1959||1760 yards||Over the course of time, the length of a yard changed several times and consequently so did the English (and, from 1824, Imperial) mile. The statute mile was introduced in 1592 during the reign of Queen Elizabeth I|
|1,609.344||mile||international||1959||today||1760 yards||Until July 1, 1959 the imperial mile was a standard length worldwide. The length given in metres is exact.|
|1,609.3472||(statute) mile||United States||1893||today||1760 yards||From 1959 also called the U.S. Survey Mile. From then its only utility has been land survey, before it was the standard mile. From 1893 its exact length in meters was: 3600/ × 1760|
|1,852||nautical mile||international||today||1852 m||Symbol: nmi; Abbreviation: NM|
|1,852.3||(for comparison)||1 meridian minute|
|1,855.4||(for comparison)||1 equatorial minute||Though the NM was defined on the basis of the minute, it varies from the equatorial minute, because at that time people could only estimate the circumference of the equator to be 40,000 km.|
|2,220||Gallo-Roman league||Gallo-Roman culture||1 1⁄2 miles||Under the reign of Emperor Septimius Severus', this replaced the Roman mile as the official unit of distance in the Gallic and Germanic provinces, although there were regional and temporal variations. |
|3,898||French lieue (post league)||France||2000 "body lengths"|
|4,000||general or metric league|
|4,190||legue||Mexico ||= 2500 tresas = 5000 varas|
|4,444.8||landleuge||1⁄25° of a circle of longitude|
|4,452.2||lieue commune||France||Units of measurement in France before the French Revolution|
|4,513||legua||Chile,  (Guatemala, Haiti)||= 36 cuadros = 5400 varas|
|4,531||Wegstunde||Saxony ||1722||1840||1000 Dresden rods||introduced on occasion of a countrywide road survey|
|4,828||English land league||England||3 miles|
|Germanic rasta, also doppelleuge
|5,000||légua nova||Portugal |
|5,196||legua||Bolivia ||= 40 ladres|
|5,152||legua argentina||Argentina, Buenos Aires ||= 6000 varas|
|5,556||Seeleuge (nautical league)||1⁄20° of a circle of longitude
3 nautical miles
|5,570||legua||Spain and Chile||Spanish customary units|
|5,572||legua||Colombia ||= 3 Millas|
|5,572.7||legue||Peru ||= 20,000 feet|
|Spain ||= 3 millas = 15,000 feet|
|5,590||légua||Brazil ||= 5,000 varas = 2,500 bracas|
|5,685||Fersah (Turkish league)||Ottoman Empire||1933||4 Turkish miles||Derived from Persian Parasang.|
|6,197||légua antiga||Portugal ||= 3 milhas = 24 estadios|
new league, since 1766
|Spain ||= 8000 Varas|
(state survey mile)
|7,409||(for comparison)||4 meridian minutes|
|7,419.2||Kingdom of Hanover|
|7,419.4||Duchy of Brunswick|
|7,420.439||geographic mile||1⁄15 equatorial grads|
|7,421.6||(for comparison)||4 equatorial minutes|
|7,467.6||Russia||7 werst||Obsolete Russian units of measurement|
|7,500||kleine / neue Postmeile
(small/new postal mile)
|Saxony||1840||German Empire, North German Confederation, Grand Duchy of Hesse, Russia|
(German state mile)
|Denmark, Hamburg, Prussia||primarily for Denmark defined by Ole Rømer|
|Austria-Hungary||Austrian units of measurement|
|9,062||average Post- or Polizeimeile
(middle post mile or police mile)
|9,206.3||Electorate of Hesse|
|9,261.4||(for comparison)||5 meridian minutes|
|9,277||(for comparison)||5 equatorial minutes|
(old state mile)
(old state mile)
|10,000||metric mile, Scandinavian mile||Scandinavia||still commonly used today, e.g. for road distances.; equates to the myriameter|
|11,113.7||(for comparison)||6 meridian minutes|
|11,132.4||(for comparison)||6 equatorial minutes|
|11,295||mil||Norway||1889||was equivalent to 3000 Rhenish rods.|
- 1066.8 meters – verst, see also Obsolete Russian units of measurement
- 3200 meters – kosh, used in North Bihar, India.
- Medieval weights and measures for various definitions of the league.
- List of obsolete units of measurement
- Portuguese customary units
- Spanish customary units
- Seven-league boots
- Trade, Travel, and Exploration in the Middle Ages: An Encyclopedia
- The Oxford English Dictionary
- Espasa-Calpe Dictionary, Argentina and Mexico Edition 1945: headword Legua
- François Cardarelli: Scientific Unit Conversion (Springer-Verlag London, 1999)
- Jules Verne: Vingt mille lieues sous les mers (1871), Part 2, Chapter VII
"Aussi, notre vitesse fut-elle de vingt-cinq milles à l’heure, soit douze lieues de quatre kilomètres. Il va sans dire que Ned Land, à son grand ennui, dut renoncer à ses projets de fuite. Il ne pouvait se servir du canot entraîné à raison de douze à treize mètres par seconde. Quitter le Nautilus dans ces conditions, c’eût été sauter d’un train marchant avec cette rapidité, manœuvre imprudente s’il en fut."
"Accordingly, our speed was twenty–five miles (that is, twelve four–kilometer leagues) per hour. Needless to say, Ned Land had to give up his escape plans, much to his distress. Swept along at the rate of twelve to thirteen meters per second, he could hardly make use of the skiff. Leaving the Nautilus under these conditions would have been like jumping off a train racing at this speed, a rash move if there ever was one." Translated by F. P. Walter
- Spence, E. Lee. Spence's Guide to Shipwreck Research, p. 32. Narwhal Press ( Charleston), 1997.
- Spence's Guide to Shipwreck Research, by Dr. E. Lee Spence, Narwhal Press, Charleston/Miami, © by Edward L. Spence, 1997, p. 32
- Vikki Gray (1998-12-24). "Land Measurement Conversion Guide". Vikki Gray. Archived from the original on 2007-06-08. Retrieved 2007-06-04.
- Cardarelli, François Cradarelli (2003). Encyclopaedia of Scientific Units, Weights and Measures. London: Springer. p. 40. ISBN 978-1-4471-1122-1.
- Leopold Carl Bleibtreu: Handbuch der Münz-, Maß- und Gewichtskunde und des Wechsel-Staatspapier-, Bank- und Aktienwesens europäischer und außereuropäischer Länder und Städte. Verlag von J. Engelhorn, Stuttgart, 1863, p. 332
- (in German) Pre-metric units of length
- Helmut Kahnt (1986), BI-Lexikon Alte Maße, Münzen und Gewichte (in German) (1 ed.), Leipzig: VEB Bibliographisches Institut, pp. 380
- "Historie der Postsäulen" (in German). Forschungsgruppe Kursächsische Postmeilensäulen e.V. und 1. Sächsischer Postkutschenverein e.V. Retrieved February 5, 2017.
- IKAR-Altkartendatenbank[ permanent dead link] der Staatsbibliothek zu Berlin, Kartenabteilung.