When Sam measures out the rope he counted out the lenght of the rope in ells. Now if you were like me when I first read this you probably said 'What the heck are ells?'.

From my understanding of Footnote 11. There is a measure called an English-ell which is equal to 45 inches. And what Tolkien first wrote was called a hobbit-ell, thinking that it would be somewhat smaller than an English-ell. But as he wanted he lenght of the rope to be just enough for the job at hand. Tolkein just called the measurement an ell, with the understanding that that was 45 inches.

Sam estimated that he had thirty ells of rope more or less. And with the understanding that 18 fathoms is 108 feet and 30 ells would come to 112 feet and 6 inches. And considering the the knot and the loop around the stump. They were cutting it very fine.

Probably the ell originated through a custom of measuring lengths of cloth using two forearms, with the hands touching or overlapping.