The "lost 116 pages" were the original manuscript pages Joseph Smith translated. These pages were lost by Joseph Smith's scribe Martin Harris during the summer of 1828 and are presumed to have been destroyed.
These lost 116 pages were handwritten on the paper of the day. If these pages were printed in the Book of Mormon as modern pages, how many pages would this be?
Zarahemla Research Foundation gives the following description of the pages.
Description of the Original Manuscript. The paper used for the Original manuscript was called "foolscap." Foolscap originally referred to a watermark of a jester's cap on writing paper. This term came to apply to writing paper which generally measured 12" to 13-1/2" wide by 15" to 17" long, whether or not it carried a watermark. The surviving Original manuscript pages are of two sizes and three kinds of paper-one, a coarse mesh machined paper, the others of finer handmade texture.
I am not sure how to take this description and turn it into the number of modern Book of Mormon pages.
In other words, I would like to know what percentage of the Book of Mormon was lost.