A bookcase with shelves allows you to organize your personal library, to display decorative accents or to neatly arrange other media like video games or Blu-Rays. Bookcases come in a wide range of sizes, so deciding how large of one you need can be a challenge. To do so, multiply the width of the shelf times the number of shelves. Then, divide that result by the average width of what you wish to store. This tells you how many of the item will fit. Also, take shelf height into consideration. If you have oversize books or media, you may need a bookcase with taller shelves or adjustable shelving.