I have in the past dispensed with a box spring and used 1/2" plywood to almost completely cover the mattress base. The advantage is that the mattress has uniform support and never shows the dents from the slats.

The main disadvantage is that 1/2" is rather heavy for taking off on a weekly basis to vacuum under the bed.

Would I get away with 3/8", or even with 1/4", plywood? My hunch is that 1/4" is plenty of thickness to support an average-weight (150-200 lb.) adult. But it has to also support the weight of the adult standing, for otherwise a simple exercise like changing the ceiling lamps would crack the base.

Rephrasing and summarizing: what is the fir/spruce plywood thickness needed to support an individual on a span of 38" (half the span of a King-sized bed)?

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    I agree with Rob below, if you're still using the slats 1/4" should be more than strong enough to bridge the gaps between them.
    – Graphus
    Jun 9, 2015 at 9:30

2 Answers 2


I would suspect that a 3/8" would be enough. If you want to screw your slats to the bottom of the plywood, you could use the 1/4" plywood. 3-4 slats would be enough to stiffen up the 1/4" to handle most of the abuse you'll be likely to throw at it.


As long as you still plan to use the slats, you can go pretty thin with whatever material you put over them to smooth out the spaces between the slats. 1/4" plywood should would work fine.

  • I would even suggest using thin manufactured material like hardboard as it won't splinter like plywood.
    – aaron
    Jun 12, 2015 at 17:23

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