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I'd like to build a desk from a sheet of wood and four metal legs at each corner. Appearance is not critical; a rugged built-from-scratch look is quite fine. Dimensions will be 1200mm x 650mm (47" x 26").

If I build this from plywood, how can I calculate how thick the plywood must be to avoid the desk bending in the middle?

In a perfect world, the desk is super strong - enough that I could sit in the middle (at 75kg/165lb). In a realistic world, it needs to hold two large monitors and various computer accessories, totalling no more than 20kg/45lb.

I've found a place that offers hardwood plywood at 15mm (0.6"), 18mm (0.7") and 25mm (1") thickness. How do I determine which thickness is sufficient for my plans?

I've assumed hardwood plywood is a reasonable choice, but softwood plywood would be 25% cheaper if I can get away with it.

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I would go with at least 3/4" (or something close to that). I would use the hardwood ply for a desk, it has a much nicer finish and will not dent as easy. The birch ply you get from the box stores is nice too.

Sitting on it.... eh, I dunno, I build one like this and it worked great for everything I needed, but I'm not sure I'd sit on it (I'm also 275 lbs). It'll hold you, but I wouldn't make a habit of using it to support body weight.

You probably need to buy at least a 4'x4' piece anyway, so if you want it to be really strong, make it 24" deep, double up the layers and trim out the front with a piece of solid oak. It'l look great and be and strong as ever.

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Most desktop thicknesses range anywhere between 1-1/4" and 1-1/2". Obviously the thicker the top the stouter it will be. As for material choice, since your desk is fairly small, I got with whatever's comfortable to the wallet!

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Close to what you need, here's a shelf sag calculator. if you imagine each end is supported, a 4' shelf of 0.6" thick ply will hold 30 lbs without issue.

If you spent a couple more bucks and added a 2x2 frame around the underside of the plywood, it would be dramatically stronger. Here's a pretty simple example video (larger but you get the idea).

  • Build a frame. What would you screw the legs to if not. – Mazura Jan 5 at 1:27
  • @Mazura I was planning to screw them directly to the desk top. (Particularly if using the inch thick plywood). These are the legs I'm thinking of. – Duncan Jones Jan 5 at 6:49
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    @DuncanJones - $20 3/4" ply and $10 in 2x4s, or +$80 1" ply and ultimately more deflection. Whatever you get, I'd suspend it between two carts at the store and bang on it like I'm typing furiously, with something 24" tall sitting on it that you're trying to read the whole time. Take two imaginary monitors close together and lean on the table, and then watch if they touch each other. Bounce and deflection are unacceptable for a desk you're going to use for hours on end. – Mazura Jan 5 at 7:06
  • @mazura Great insights, thanks. Think I’ll go down the frame route then! – Duncan Jones Jan 5 at 13:17
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    @DuncanJones - It'd be better if it were 1/4", ~2" long lag screws into an additional rib of the framing, at w/e distance from the edge that you want the legs. Anything I consider a 'surface' had better be ready for two idiot teenagers to jump on. – Mazura Jan 5 at 21:58
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You could glue and screw ( from the bottom ) two, or more, pieces together to make a thicker top. I did this with Appleply for a corner desk, it has no voids in the laminates, so you can leave the edge visible.( i had to come up with plan b, i paid for thicker stuff but the retailer sold mine before i picked it up, so to make a dead line i glued two 1/2" pieces they gave me. )

You can just glue a strip of the nicer stuff around the perimeter and use a lower grade to fill in the bottom.

If you really want to stiffen it up you could screw on a piece of angle iron underneath to give it strength.

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I built a hardwood 3/4 ply desk not to long ago and edge banded it with solid birch. It also had plywood base that the legs were attached to and the desktop rests on. It is plenty strong.

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