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I would like to determine the weight capacity of a cabinet made of 1/2" plywood which is 18" deep and 60" long, 37" high.
The cabinet has 2 sides and 2 uprights spaced about 20" from either end. The top is also 1/2" plywood.

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    “ What Is the Airspeed Velocity of an Unladen Swallow?”
    – Alaska Man
    Commented Mar 30, 2020 at 8:45
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    @AlaskaMan African or European?
    – user5572
    Commented Mar 30, 2020 at 13:30
  • You are probably never going to get a definitive answer to this question, as there are just too many unknowns. Wood, even plywood, is a variable product. Unless you are building patrol boats for a Navy (and I suppose they use reinforced plastics for that now) you aren't going to have reliable stress and failure data to work from. There are engineering data for wood out there, and you might find some references if you search previous Q&A. The general answer to your main question is "quite a lot, actually. But what are you intending on supporting?"
    – user5572
    Commented Mar 30, 2020 at 13:35
  • Voted to close as it's impossible to give a definite Answer to this (even with far more detail about the construction). And in case it's not also obvious the manner of fixing it to the wall could turn out to be the weak point, not the cabinet itself.
    – Graphus
    Commented Mar 30, 2020 at 13:45
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    By the way, welcome to the site and please don't view the "votes to close" as a personal attack. I honestly hope that you continue asking questions here as you continue with your journey through woodworking.
    – SaSSafraS1232
    Commented Mar 30, 2020 at 15:56

3 Answers 3

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Given the information offered the only way to arrive at an answer is (as mentioned in the comments) to experiment with different weights and see what works.

Big Bang Method
If over loading the cabinet will not cause a catastrophic event - hurting someone or damaging something you care about - you could load a large amount of weight and then periodically observe the cabinet for bending / breakage. Let the weight sit for some period of time and check again. Personally, this method makes me nervous.

Slow but Steady Method
A more cautious method would be to start with low weight items - observe over a period of time (say once each hour for example) and increase the weight a little - observe and repeat until the ideal weight is found.

Be sure to identify the part of the cabinet that connects to your house. If the cabinet sits on the floor you will want to observe the parts of the cabinet that transfer the contained weight to the floor. If the cabinet is mounted to the wall you will want to observe the wall mounts.

One way to go at it would be to determine how much weight you need it to hold.
If you only need it to hold a few pounds the materials in the cabinet can handle that as long as the weight in the cabinet is transferred well to the house (floor or wall).

If you need it to hold as much weight as you can stuff in then do some testing.

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  • What your methods will not find is how those shelf spans will sag over time. Plywood has a way of imperceptibly sagging over time in a manner than can't really be modelled easily. Really, I don't think we have neough information in the original question.
    – user5572
    Commented May 19, 2020 at 16:11
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Try the sagulator. While I wouldn't hang my hat on it as, jdv mentioned, each piece of ply will be different, it'll give you an idea if the weight you want to put on it is in range or not. https://www.woodbin.com/calcs/sagulator/

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  • The downside to link-only answers is that links will be dead in an internet moment, rendering this answer less useful in the future. I'd reword this to say that there are a few calculators on the web so at least someone has search terms that once worked for you. But there is no getting around the fact that such sites will eventually go away, and the content cannot be provided here as a synopsis.
    – user5572
    Commented Apr 13, 2020 at 15:11
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If your wall studs are 16" on center, 64" equals 4 studs on center. A 66" cabinet would allow for a pattern of 4 screws per row, with a total of 3 screws at 6" spacing for up and down rows. Using 3" stainless wood screws, with a 60" cabinet you would only hit 3 studs at 16" O.C. (16", 32", 48") you would want to open the wall to add support backing, with whatever material your wall studs are, patch the walls up, or using wall anchors (which I don't recommend for this project). Hope this helps/

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  • Oops, would be 3 screws at every 12" on the up and down pattern, not at 6".
    – Mark Rode
    Commented Apr 12, 2020 at 12:12
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    I don't think the original question was about the strength of hung cabinets on a wall. Rather, it was about the deflection strength of plywood in the cabinet.
    – user5572
    Commented May 19, 2020 at 16:09
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    Remember you can always edit your question. It isn't necessary to make edits in comments.
    – user5572
    Commented May 19, 2020 at 19:16

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