# How can I estimate the load capacity of a set of shelves?

I'm pricing and researching supplies for built-ins in my living room. The plan is cabinets on the bottom, a cubby for a TV and staggered shelves for several hundred HEAVY books above that. My instinct is to build the whole thing out of 3/4" birch ply, but I'm also looking at pre-built wall cabinets for the base to possibly save myself some hassle.

This leads to a number of questions about material choice and structural design. For instance, could a couple IKEA wall cabinets be the base for a structure that will hold a thousand pounds? Two thousand pounds? (I'm aware the floor has to support this as well - I'm on a slab.)

So, based on materials, joints, and structure, how can I estimate how much a piece of furniture can hold? How much weight can a box-frame support? At what span will a shelf of material X fail? Are there tables or online resources available for this sort of thing?

• The Ikea cabinets may have max load information on the packaging or assembly manual. For example, this bookcase lists its max load per shelf as 66 lbs near the bottom of the page on the product information tab. – Doresoom Sep 16 '11 at 14:04
• @Doresroom - good info. Is there a difference between what a bookcase can hold and what can be placed on top of it? Is the top equal to a shelf? – Steve Jackson Sep 16 '11 at 14:31
• There should be some difference, since the shelves are only supported at the ends, and the top has the upright side pieces to support the load. So if you place the loading at the ends of the bookcase, it may add a little bit of capacity. I'd be wary of exceeding it by much though, because MDF isn't the strongest material out there. I don't think I would trust that particular bookcase with a max loading of over 300 lbs. (Rated loading is 264 lbs counting the top as a shelf.) – Doresoom Sep 16 '11 at 15:20

There are a number of online calculators related to the problem in the answers & comments to an earlier question about building shelves:

References included:

All of these were to calculate sag -- wood and metals are going to sag before they collapse in most cases. The exception would be when fasteners tear out the side of wood (eg, an anchor comes free from the wall), and sometimes, there isn't a whole lot of time between sag & fail (I had a bookshelf bow, pull free from the shelf supports, and then cascade as it took out all of the other shelves below it).

Concrete will fail explosively (sudden collapse with little to no warning, which is why reinforced concrete specifically has less than the optimal amount of steel in it, so the steel goes first), but that's not normally used for shelves.