We recently had a professional build our kitchen cabinets, and noticed after we paid them in full that the shelves inside the upper cabinets were only 5/8" thick. We applied pressure to the middle back area of the shelves and they flexed downward. Shouldn't shelves be 3/4" thick for rigidity and strength?

  • 1
    Think it would depend on the selves length. Think the only selves I have that are 3/4, is a small bookcase with over 5 or 6 feet between supports. Most of the others are 1/2 or 5/8 inch thick.
    – crip659
    Commented Aug 6, 2022 at 14:43
  • The longest shelf span is 30" . They are adjustable shelves with no support underneath; concerned the adjustable pins might pop out when too much weight is on them, not to mention that they dip in the middle when pressure is applied.
    – RET
    Commented Aug 6, 2022 at 14:58
  • They should last, mine have lasted over 30 years, and sounds like standard cabinet construction. Will depend on the quality of the shelves themselves and the amount of weight on them.
    – crip659
    Commented Aug 6, 2022 at 15:09
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    It depends on the material, and for that, ask the cabinetmaker. If it is particle board with a covering of melamine or faux wood grain it will sag on its own over time. If it is a solid wood shelf, depending on the specie of wood, it will bow with weight applied, and may stay that way over time. If it is a strong wood like oak or fir, it will do what you need. It may bow under a big load, but will return once the load is removed.
    – Jack
    Commented Aug 6, 2022 at 15:11
  • 1
    What did your contract with the builder specify?
    – JACK
    Commented Aug 6, 2022 at 15:13

1 Answer 1


TLDR: 5/8" plywood shelves spanning 30" are fine. They aren't going to fall.

5/8" shelves might seem a little slim, especially when you've been primed to think that 3/4" are better, but under normal loads, these should be fine. (Assuming plywood -- particle core is a different matter, and you can probably see what the actual core is by looking at the back of the shelf.)

They aren't going to flex themselves off the shelf pins and cascade down.

If you end up storing your collection of osmium or tungsten up there, then the shelf might sag a little and somebody will install a 1x2 of hardwood, oriented vertically, at the back of the shelf and that problem will go away.

edit: just to add mention of a very useful tool: the Sagulator that says a 30" wide, 12" deep, 5/8" ply shelf with 30# per foot uniformly distributed will sag .02" (<2mm) or less.

  • 2
    If the sag becomes permanent and noticeable, you might want to turn the shelf over. That will remove the sag. Commented Aug 7, 2022 at 1:17

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