Dado joint and groove
A dado is a square, flat-bottomed slot cut across the grain of one board to take the end of another, like a shelf in a bookcase side. A groove is the same slot cut along the grain, for a drawer bottom or a panel. The slot holds the shelf up and keeps it square, which a plain butt joint can’t do.
How deep
A dado is traditionally cut no deeper than half the thickness of the board it is cut into.
A dado takes wood out of the side that carries the load, so its depth is kept to a fraction of the board’s thickness. In 3/4 in stock that means no more than 3/8 in. Fine Woodworking puts the usual target nearer a third.
Traditional rule, stated by Fine Woodworking (Taunton Press) and Woodcraft
Width and plywood
The dado should be as wide as the shelf is thick, which for plywood is often not its nominal size. Measure the actual sheet, then set the dado stack or pick an undersize plywood router bit to match it, and test the fit in scrap first.
How it’s cut
On the table saw a stacked dado set cuts the width in one pass, and the fence or a sled sets the position. A router with a straight bit and a clamped-on fence or a straightedge cuts dados in large panels that are awkward to move over a saw. By hand, the sides are sawn to depth, the waste chiselled out, and the bottom levelled with a router plane.
Stopped dados
A stopped dado ends short of the front edge so the joint can’t be seen from the front, and the shelf is notched to fit around the end. A router cuts these more easily than a saw, because it can start and stop anywhere along the cut.
Related joints
Sources
- Fine Woodworking (Taunton Press), Mario Rodriguez, "All About Rabbet and Dado Joints" (2005), read 2026-11-07
- Woodcraft, Craig Bentzley, "Joinery Made Simple: Rabbets, Dadoes, and Grooves", read 2026-11-07
Proportions marked as a traditional rule are shop tradition, not measurements. This site gives no joint-strength numbers: the published tests each used a different rig. How we source these numbers.