
maybe start with measuring the width, height, and depth of each shelf (if it’s one large unit, just divide the length in thirds or something to reflect 3 individual units) and compare your measurements to the billy ones or target ones (similar to billy but no option for additional shelves). then if you really needed to, i’d count all the books and divide it by say 5 (the amount of shelves per unit) to see how much would fit on each unit (i think. i suck at math)
It has more, it’s a small house with an extra bedroom that I’m converting into a library/reptile room (worried about humidity tho so that may change). Rn I have a little nook built from knocking down the wall between my room and the attic above the garage about 8x8 ft. Because of this the room has a triangular back wall and all the shelves are different lengths, widths, and heights so it’s hard to get a good estimate. And I’m running out of space so some shelves have two rows of books
In that case, I would recommend getting as many shelves as you think will fit comfortably in the new place. It doesn’t hurt to have a little extra space to display things or for future books, and if you end up with one shelf too many for the room, you can always put it in another part of the house🤷♀️