Thickness to resist sag
The biggest pitfall with a wall shelf is sag under load. For a shelf up to roughly 24 to 32 in wide, 3/4 in is usually enough. If you want it wider or want to load it heavily (books, plants), step up to a thicker material, glue two panels together, or add a center support. A thicker shelf also reads as sturdier as a floating shelf.
Depth
Match the depth to what goes on it: 6 to 8 in for decor and picture frames, 8 to 12 in for books. Too deep looks bulky and pushes far into the room.
Mounting it invisibly
For the floating look, use hidden shelf brackets: steel rods or a concealed bracket you screw to the wall, then slide the shelf over them. Drill the holes into the back edge of the shelf to match. Pick anchors that suit your wall (concrete, masonry or drywall) and the load. On drywall, hit the studs or use rated heavy-duty anchors.
Material and finish
Plywood sags the least and has a clean edge. Finish the cut edges with a clear coat or edge banding. Read up on the options in choosing sheet material.
Cut several shelves from one sheet with little waste. Making more than one wall shelf, or a whole set? Enter them in cutlistlab's free tool and nest them out of your sheet goods with the least waste. Handy: leftover offcuts get saved for your next project.
Frequently asked questions
How thick should a wall shelf be?
For a shelf up to roughly 24 to 32 in wide, 3/4 in is usually enough. For a wider or heavily loaded shelf, step up to a thicker material, or glue two panels together for a stiff, chunky floating shelf.
How do I hang a floating shelf with no visible brackets?
Use hidden shelf brackets: steel rods or a concealed bracket you fasten to the wall, then slide the shelf over them. Drill matching holes into the back edge of the shelf. A thicker shelf hides the rods better.
What material for a wall shelf?
Plywood is strong and stiff and resists sag, with a clean edge. Solid wood or a thick glued-up panel gives a rugged floating shelf. Melamine board looks tidy but sags a bit sooner, so keep the span short.