If I made a 3/4 plywood table with simple metal legs from amazon, do I need to add more supports?

Baltic birch is strong. If you first drill a hole and turn the screw in it then this will suffice in most cases, and a apron isn’t necessary. With heavy loads however you make it much stronger with an apron. In short: With light use direct screwing may be sufficient.

-- https://dutchypatterns.com/

I agree with Dutchy, but I would add that where you position the legs is critical if you want to avoid additional support for the top. If you place them near the ends of the table, you will almost certainly see your plywood top sag in the middle, even under a light load: I’m sure there is data available on leg placement on such tables, but I don’t have any at my fingertips. You might want to do some research or simply run some tests to determine which placement works best for you.

Check the Sagulator. It does not specifically give Baltic Birch as a choice but might give you an approximate idea of sag, etc.
I built a 4 ft x 8 ft table from 3/4” ply (not BB). I put a 2×4 apron all around. Used for a dining room table for a large crowd….no problem with sag.

Plywood alone IMO will sag. You will need some support for the length and the width.

https://www.lumberjocks.com/topics/317719

Isn’t this the same question that has been answered?

Never design a table for the lightest possible use. Consider also the side forces on the leg screws. Will they rip out?

-- You know, this site doesn't require woodworking skills, but you should know how to write.

Plywood is more “bendy” than solid wood. For a table of that size I would brace it, if it was mine.

-- Bondo Gaposis

If you are going to build a table, do it the right way. An apron all around will prevent the plywood from sagging in the middle. Keep the apron about 3” in from the edges of the plywood and add a cross brace halfway on the long dimension. The edges should also be edge banded if appearance is needed.

How far in from the outer edge will the legs be installed, what will the load be and where will it be located. This is a simple statics problem but all variable need to be established before an answer can be determined. This would sag very little under its own weight but could be quite a big more if you’re using it to rebuild marine engines upon.

-- “I never in my life thought I would have to say this, but the proper role of government is not to fund the distribution of crack pipes,” Lauren Boebert

damn that guy copy pasted my entire question, and stole my username

https://www.lumberjocks.com/topics/317719

Isn t this the same question that has been answered?

- CommonJoe

I’ve got a 40”x72” 3/4 CDX table with a 1×1.25” fit around it (hides edge of plywood in a rabbit). But my “legs” have always been 16” wide boards or angle iron set in 12” from the ends. No warp or sag after daily use for the last 30+ yrs.

Obviously your numbers are different, but believe that leg placement will matter greatly in your design…