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Which Bookcase Do You Need? Calculate the Capacity of a Book Shelf

Anyone can Google to find a quick answer. But sometimes, the simplest answer isn't the smartest. JK enjoys big questions and interrogations.

How do you build the perfect bookcase?

How do you build the perfect bookcase?

How Many Books Fit on a Bookshelf?

Maybe you're looking at a giant pile of books, wondering how big a bookshelf you need to buy. Or maybe you're looking at a bookcase, in a store, or online, wondering how much of your library it will hold. Perhaps you're good with your hands and planning to build your own custom shelves.

In any case, you can make a fairly accurate estimate of what you'll need, even if you're not great with numbers. All you need to do is take some measurements and do some simple math.

How to Calculate a Bookshelf's Capacity

How can you find out how many books will fit on the shelf your grandfather built?

  1. First, get a tape measure to find out how wide each shelf is. Measure the open space inside the shelf, not the wood that frames the opening. The average standard width of a bookcase is 30" to 36", but custom sizes vary.
    For example, let's say your grandfather's bookcase is 38" wide.
  2. Next, multiply that number by the bookcase's total number of shelves.
    Let's say your grandfather's shelf has nine shelves. So 9 x 38 = 342.
  3. Next, you'll need to gauge the approximate average width of your books and divide it into the number you found in step #2. Most books are about an inch and a half thick, but things like art, medical, and reference books tend to run a little fatter. Magazines tend to run about a quarter of an inch. If you're a perfectionist, you'll add up the exact widths of all your books (!!!) and divide by the total number of books to get the average width. If you're lazy like me, you'll make a rougher estimate and deal with the excess (or lack) of space later.
    Let's say the average width of your books is about 2". So 342 ÷ 2 = 171. Your grandfather's bookshelf will hold approximately 171 books.

How to Calculate the Average Width of Your Books

How to Build or Buy the Perfectly-Sized Shelf for Your Books

But what if you're starting with books but no shelf? If you want to make sure that the bookcase you buy or build is big enough for the books you own, read on.

  1. First, count how many books you have. Let's say you own 200 books.
  2. Next, you'll want to estimate their average width. Again, you can do this the nitpicky way by measuring each book's width, adding them all up, then dividing by the total (200), or you can make a rougher guess. Let's say that your books average 3" in width.
  3. Multiply the average width with the total number of books (3 x 200 = 600). This means you have 600 inches total width of book, so you'll need 600 inches of shelf.
  4. If you're building your own, you have some freedom and flexibility. All you need to do is make sure you build at least 600 total inches of shelf space.
  5. If you're buying online, multiply the bookshelf's width and the number of shelves it has to find out how much space it offers. The ubiquitous IKEA Billy bookcase, for example, runs almost 30" wide and has 6 shelves. Which means it offers just under 180" of shelf. If you need 600 inches of shelf, you'll need 3.33 bookshelves (600 divided by 180). So you can buy 4 and use the extra space to display your collection of Star Wars figurines, or you can donate 10% of those dusty textbooks to a thrift store.

© 2017 Jo Kenyon