Formula for Plywood Thickness?

I’m building some furniture for my son — bed, headboard, bookshelves. We’re going to use plywood. Is there a formula for determining what thickness of plywood I should use? I can guesstimate it by looking at the thickness and how much I can get the large sheet to bend, but is there a rule that determines what thickness is needed for given dimensions and expected load?- Chip McDaniel

Tim Inman: From your question, it sounds as though you are wanting to make curved or bent surfaces. Without knowing more, it is very difficult to give good advice. However, if you are wanting to make pieces with significant curves, I’d suggest using a product called “bending ply” for your lay-ups. For serious work, I’d laminate multiple pieces of 1/4 inch bending ply to get the curve, and the thickness, you’ll need for your structure.

Chris Marshall: I’m going to approach my answer from the standpoint that you are only talking about load ratings for plywood and not about bending it to make curved rails and so forth. I’d use 3/4-in.-thick plywood for all of your furniture parts except for the back of the bookcase. You can use thinner plywood there, but that will depend on your bookcase design and how sturdy you build the rest of the case. In regard to the bed frame, I’d use 3/4-in. plywood to support the mattress and box spring, and I would consider how to stiffen that surface even more with cross rails. Keep it stiff, sturdy and, consequently, safe.

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