| Nautical leagues (nlea) | Leagues (lea) |
|---|---|
| 1 Nautical league | 1.15077944802 lea |
| 2 Nautical leagues | 2.30155889605 lea |
| 3 Nautical leagues | 3.45233834407 lea |
| 4 Nautical leagues | 4.60311779209 lea |
| 5 Nautical leagues | 5.75389724012 lea |
| 10 Nautical leagues | 11.5077944802 lea |
| 20 Nautical leagues | 23.0155889605 lea |
| 25 Nautical leagues | 28.7694862006 lea |
| 50 Nautical leagues | 57.5389724012 lea |
| 100 Nautical leagues | 115.077944802 lea |
| Reference | Nautical leagues (nlea) | Leagues (lea) |
|---|---|---|
| A sheet of A4 paper (long side) | 0.0000534557 nlea | 0.0000615157 lea |
| Average adult human height | 0.000305976 nlea | 0.00035211 lea |
| A football pitch (length) | 0.0188985 nlea | 0.021748 lea |
| A marathon | 7.59449 nlea | 8.73959 lea |
| Height of Mount Everest | 1.59269 nlea | 1.83284 lea |
The nautical league is a unit of length equal to three nautical miles, or exactly 5556 metres. It is longer than the land league by about 728 metres, since it is built from the nautical mile of 1852 metres rather than the statute mile.
The unit belonged to an era when it was the practical measure of coastal jurisdiction. The cannon shot rule, articulated in the seventeenth and eighteenth centuries, held that a state's authority extended as far as it could defend from shore, conventionally taken as three nautical miles. That distance became the standard territorial sea limit and was expressed as one marine league. Many older treaties and statutes define maritime boundaries in leagues for this reason.
The three-mile limit held for centuries before eroding through the twentieth. States progressively claimed wider waters, and the United Nations Convention on the Law of the Sea settled the matter in 1982 by establishing a twelve nautical mile territorial sea and a two hundred mile exclusive economic zone. Both figures are stated in nautical miles rather than leagues, and the older unit fell out of legal use.
Charts and pilot books from the age of sail used the league routinely for describing offshore distances and the visibility of landmarks. Reading those sources accurately requires knowing which league is meant, since the same word could refer to a land league, a marine league or a Spanish or Portuguese variant, and the differences are large enough to matter when reconstructing a historical position.
Today the unit has no navigational role. Charts are marked in nautical miles, and distances at sea are quoted the same way. The nautical league appears only in historical and legal texts.
The unit also underlies a familiar figure in visibility calculations. From a height of about three metres above sea level, the horizon lies roughly one nautical league away, which is why the three-mile limit corresponded loosely to what a lookout could see as well as to what a gun could reach.
One nautical league equals 3 nautical miles, 5556 metres, 5.556 kilometres, or about 3.452 statute miles.
The league is a unit of length equal to three miles, 24 furlongs, or exactly 4828.032 metres. It is obsolete in every practical sense, surviving mainly in literature and in historical documents.
The unit originated as a measure of how far a person could walk in an hour, which explains both its rough magnitude and its variability. Ancient and medieval leagues differed widely between regions. The Roman leuga was about 2.2 kilometres. French, Spanish and Portuguese leagues each had their own values, and the Spanish legua used in colonial land grants in the Americas differed again, complicating the interpretation of old property records in Texas and the American southwest.
English usage settled on three miles, a figure that was never especially precise in practice because it depended on the mile in force at the time. Since the mile itself was fixed at 5280 feet in 1593, the league inherited that definition, giving the modern value of 4828.032 metres.
Its cultural persistence far exceeds its practical use. Jules Verne's Twenty Thousand Leagues Under the Seas measures a journey rather than a depth, a distinction frequently lost in casual reference: twenty thousand leagues is roughly 96,000 kilometres, more than twice the circumference of the Earth and vastly greater than any ocean depth. Seven-league boots appear in French fairy tales as a device for covering ground in single strides. Tennyson's Charge of the Light Brigade opens with half a league onward.
The unit was formally abolished for trade in the United Kingdom long ago and has no legal standing. It appears occasionally in nautical contexts, where the marine league of three nautical miles is a separate and slightly longer unit.
Because the unit is so variable across languages and centuries, translations of older works can mislead badly. A distance given in leagues in a Spanish colonial document, a French medieval chronicle and an English statute may differ by a factor of two, and historians working with such sources generally convert to modern units and state which league they have assumed.
One league equals 3 miles, 4828.032 metres, or 4.828032 kilometres. A brisk hour's walk covers rather less than one.