Also included are songs, time lines and calendars. Where else could you find out quickly how long an Ent-stride was.
As the Ents travelled through Fangorn Forest, they measured the distances they travelled not in yards and miles, but in Ent-strides. The exact distance of an Ent-stride is never specified in detail, but what notes we have suggest that a single stride for Treebeard would cover approximately four feet (about 1.2m). By that approximate calculation, one mile would be equivalent to 1,320 of his Ent-strides. However, since the Ents seem to have been of varying sizes, it would seem that Ent-strides must also have varied in length from Ent to Ent.
The are only two known distances given in Ent-strides, and one of those is rather vague. The first is Treebeard's stated distance between the hill where he first encountered Merry and Pippin, and his Ent-house at Wellinghall. This journey took seventy thousand Ent-strides, corresponding to just over fifty miles. Later Pippin tried to count the Treebeard's Ent-strides as he travelled to Entmoot, but only managed to reach about three thousand: in other words, he lost count after a journey of less than two and a half miles.
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Encyclopedia of Arda