Bookshelf Size Calculator (Free Tool With Materials Needed & Cut List)

Enter your room’s wall size and what you’re storing, and this bookshelf size calculator will give you the dimensions, shelf spacing, and a full cut list of materials you need to build it.

How the Bookcase Calculator Works

To get started, you need to provide three pieces of information: the amount of wall space you have, the items you plan to place on the shelves, and the material that the shelves are to be made from. With these details, the tool calculates a bookcase that fits your available space and won’t collapse or bend under the weight.

Step 1: It trims your available wall space to a real bookcase size – Most walls are almost never square, and floors are almost never flat, which is why this calculator deducts a little from each side (half an inch by default) and also from the top (one inch). This gap enables the finished case to slide into position without rubbing against the paint. Both of these settings can be altered under the Advanced options.

Step 2: It splits the width into sections based on shelf sag – The section that most people leave out is the one that determines if your shelves will look like smiles in two years. All materials have a maximum span beyond which they begin to bow when carrying books; the calculator works by dividing your width into as many sections (bays) as necessary to ensure that each shelf stays within that limit. If you’re building with solid lumber, our guide to the best wood for shelves compares the strongest options.

Oversized books and vinyl are heavier per foot, which means that the spans are reduced by 10% and 15% respectively. A 72-inch wall made from 3/4″ plywood ends up with three bays, each about 22 11/16 inches wide internally. If you use MDF instead, you still get three bays, but they are nearer to the limit.

Step 3: It spaces the shelves for what you’re storing – Each type of storage has a predetermined opening height and shelf depth. The calculator works by fitting as many openings as possible into the height that remains after allowing space for the toe kick and the top and bottom panels, and then distributes any additional space equally so that all the openings are the same. Shopping instead of building? Compare your results with these standard bookcase dimensions.

If you want a particular number of sections or shelves, you can set that number yourself in the Advanced options. The calculator will still warn you if your choice causes a shelf to extend beyond its safe range or if the openings become too short for your books.

Step 4: It gives you a cut list – The list of materials is based on a typical construction method involving sides that go all the way to the floor, a toe kick set in between the sides, fixed top and bottom panels, shelves that are cut 1/16 inch shorter so that they can be easily inserted, and a 1/4″ plywood back that is fitted into the rabbets. The amount of sheet material given allows for around 20% to account for waste and poor cuts. When you are using dados or a face frame, you should modify the shelf lengths to correspond with your joinery before making any cuts. If you’d like to see it in 3D first, woodworking design software makes that easy.

The figures given for capacity and weight are only approximations; since book sizes can vary greatly, take “~300 books” to mean approximately that number rather than as a guarantee.

Tips for Buying a Bookcase

In product photographs, most bookcases appear identical; the differences only become noticeable after about six months, when the shelves are full.

• Determine what material the shelves are made from. Many budget models use particleboard or melamine of 5/8″ thickness. This is suitable for paperbacks and for decorative purposes. The shelf will bend if you load it with hardcover books. If the listing fails to state the material, then assume it is particleboard.
• Look at the shelf span rather than just the total width. A cabinet that is 36 inches wide and has no central divider has about 34 inches of shelf that is not supported, which exceeds the limit except in the case of solid wood.
• Look at the depth given. Certain brands give the external depth while others give the internal depth. An overall bookshelf depth of about 10 to 12 inches is suitable for the majority of books, but when the depth is less than 9 inches hardcovers begin to project from the front.
• Look at the back panel. It’s a thin hardboard back held in place by small nails, which offers very little resistance to the case racking; but one that is screwed on or fitted into grooves makes the entire case much stiffer.
• Count the adjustable shelves. Installing fixed shelves at 12-inch intervals is acceptable until you have acquired one of those larger coffee table books; the pin holes, which run the full height, let you change your mind if needed.
• Ensure that the bookcase comes with wall anchor hardware since any bookcase over about 30 inches in height should be anchored. If a kit is not included, buy one as they are inexpensive.

One more thing before you click ‘buy’: check how the item fits as it moves into the room. The bookcase, which is 7 feet tall and shipped assembled, has to go up the stairs and around the landing first. Our furniture dimensions guide has sizes for everything else going into the room.

Tips for Building a Bookcase

Measure your actual plywood – Plywood marketed as 3/4″ in thickness is generally actually 23/32 inch thick, the thickness sometimes being less. This may not seem like a great deal; it makes the difference between a tight dado and a loose one. So use calipers to measure a piece of scrap and cut your dados to match that measurement, not to the figure on the label.

Check the tilt-up clearance before you build tall – It tends to catch people’s attention. When you build a bookcase on the floor, you have to tip it up, and while it’s tipping, the diagonal of one side must clear the ceiling. A bookcase that is 84 inches high and 12 inches deep requires approximately 85 inches to stand upright. One that is 95 inches high and 14 inches deep needs just over 96 inches, which means it won’t be able to stand under a standard 8-foot ceiling. If you’re planning to have the bookcase near the ceiling, then you should construct it from two stacked sections or arrange to assemble it while it’s standing, and fill the gap at the top with a trim piece.

Stiffen the shelf edges – Attaching a 1×2 piece of hardwood to the front edge of each shelf has two purposes: it conceals the layers of plywood, and it greatly increases the stiffness of the shelf. This is the cheapest solution available for a span that is nearly at its limit.

Drill shelf pin holes with a jig – Freehand drilled hole spots are not completely level and the tilt will be visible on each shelf. A shelf pin jig having a 32mm spacing and 5mm pins is cheaper than a sheet of plywood and ensures that the holes align on both sides.

Plan around the baseboard – When the case is fitted tightly against a wall, the baseboard will be pushed forward by at least one-half inch. In this situation, you can notch the back bottom corners of the sides so that they fit over the wall, or else pull the baseboard in that area and reinstall it around the finished case; for built-in bookshelves, the second option looks better.

Put the tall openings at the bottom – The largest and thickest books should be placed on the lower shelves since this reduces the weight and thus makes the cabinet more stable, and it also prevents you from lifting a 6-pound art book over your head; you should bring the adjustable shelves closer together as you go upwards.

Anchor it, even if it feels solid – Drive the screws through the back or top rail into at least one wall stud, and into two if the bookcase is wider than about 32 inches. Since a complete bookcase can weigh more than 600 pounds, it is most likely to tip when the lower shelves have been emptied and someone pulls on the top shelf.

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