Bearing Capacity of Glass Shelves

... is not much. Here are a few details. May 22, 2006

Question
I need to put glass shelves in a frameless 42" upper dish cabinet but I am nervous about their weight-bearing capacity. What thickness of glass would you recommend and is support at only the two ends sufficient?

Forum Responses
(Cabinetmaking Forum)
From contributor A:
That would depend on how wide the case is and what will be put on it. You should plan for the worst possible scenario with the weight.

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From contributor B:
Wood magazine published a chart for this in the March, 2004 issue at page 54. I know this, because I photocopied it and keep it in my briefcase as a reference tool. According to the chart a 1/4"-thick piece of glass, spanned at their maximum of 36 inches, can carry only 5 pounds. A similarly long 3/8" piece of glass can bear 18 pounds and a 1/2" piece can bear 33 pounds.

Their chart demonstrated how the weight bearing capacity decreases as the span widens. (i.e., a 12-inch wide shelf at 1/2" thick can bear 345 pounds, the same shelf at 2' wide can bear 81 pounds and a 3' span can only bear 33 pounds). These measurements are for annealed glass only supported at the two far ends. Your example, being 42" wide, means that you're probably at the (pardon the pun) break-even point. A 3/8" piece of glass that long will look nice and light but will likely only be able to bear a maximum of 3-5 pounds of weight.

I'd figure out how to get a center support in there somewhere, or build a wood or metal picture framework and use that to buttress the glass. Your 42" is an awful long area to trust to just glass.

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From contributor C:
I am copying this for future reference. We did 3/8” thick tempered glass shelf’s for a 37-½” span a while back. It felt fine after the china was loaded but I would be nervous about going longer with 3/8” A partition behind each door is the best solution. We also used heavier shelf supports than the standard 5mm.

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From the original questioner:
I will either put a support in the middle or use an additional support frame as suggested.

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From contributor D:
I would add that the maximum sizes listed are a mite small. Keep in mind that glass is a liquid and will eventually bend under load.