When the Spanish came to explore the New World, they calculated distances in leagues. This unit of length is no longer officially used by any nation. Today, we use metric or US standard, sometimes called imperial. (Need to convert metric to standard or the other way around? Click here.)
Originally, a league was calculated by how far a person could reasonably walk within one hour. Different countries had varying results. Persia, Rome, Bolivia … you can imagine the difficulty a foreign visitor would have in understanding how far it was to the next happy meal. Standardization is the inevitable outcome.
However, China, which officially adopted the metric system in 1984, still uses the term li to describe distance where the Great Wall of China is the ten-thousand-Li-wall, or wall of immeasurable length. And in Mexico, the term league is still used to explain how far one can expect to travel in a mountainous region versus flat terrain.
In J. R. R. Tolkien’s Middle Earth, a league is three miles. That’s a fair estimate of the truth.
As I research topics of European expansion, since I am familiar with standard measurement, I use a quick mental calculation of 2.5 miles per league. Again, it’s a rough estimate, not an exact measurement, but this helps me visualize approximately how far the explorers would have traveled. To be more accurate, multiply one league by 2.6 miles or 4.2 kilometers. To be precise, use a conversion service or comparison website.
A nautical mile measures length by time and arc, and is primarily used in polar expeditions, aircraft travel, and, as the name implies, travel by sea.
Then there’s the definition of league as an association of people interested or involved in a similar pursuit, such as a sports league or League of Women Voters.
But for my purposes, when I read that a river is two leagues wide, I think about the distance I have to travel to go grocery shopping: about five miles.