Mortise and Tenon Joint

The mortise and tenon is one of the oldest joints in woodworking and still one of the strongest, used to join pieces at an angle — most often a rail into a leg or a stile into a rail — for furniture frames, doors, tables, and every structure in between that needs to actually hold together.

How It Works

A mortise is a rectangular cavity cut into one piece. A tenon is a matching tongue cut on the end of the second piece, sized to fit snugly into the mortise. Glued together (and sometimes further secured with a peg through both pieces, called "draw-boring" or "pinning"), the large glue surface area and mechanical interlock make this joint highly resistant to both racking and pulling apart.

Proportions

A common rule of thumb sizes the tenon's thickness at roughly one-third the thickness of the material it's cut from — thick enough to have real strength, thin enough to leave solid mortise walls on either side. The tenon's shoulders (where it meets the full width of the workpiece) help resist twisting and hide any minor gaps at the joint line.

Common Variations

• Through tenon — the tenon passes completely through the mortised piece and is visible on the far face, sometimes deliberately left slightly proud and trimmed flush, or wedged (see below) for a joint meant to be seen and never disassembled.
• Blind (stopped) tenon — the mortise doesn't go all the way through, so the tenon is hidden once assembled; the standard choice wherever the joint shouldn't show on the far face.
• Wedged mortise and tenon — a through tenon with a saw kerf cut into its protruding end, into which a wedge is driven after assembly, splaying the tenon's end outward inside the mortise for a joint that mechanically locks itself rather than relying on glue alone. A traditional choice for joints meant to be permanent and load-bearing, like a workbench's leg-to-top joint.
• Haunched mortise and tenon — the tenon keeps a short, stepped-down haunch alongside its main body, used wherever the joint runs into a groove cut for a floating panel (a frame-and-panel door's corner, most commonly) — the haunch fills the gap the groove would otherwise leave at the outside edge of the frame.
• Open-slot mortise — used in a bridle joint-adjacent situation where the mortise is open on one edge rather than fully enclosed, generally easier to fit and adjust than a closed mortise at some cost to overall joint strength.

Cutting the Joint

Mortises can be cut with a chisel and mallet, a drill press with a hollow-chisel mortising attachment, or a plunge router and template. Tenons are typically cut on a table saw with a dado stack or tenoning jig, or by hand with a saw and chisel for cleanup. Whichever method is used, a snug (not forced, not loose) fit is the goal — a tenon that requires a mallet to seat is generally too tight and risks splitting the mortise walls.

Wood Movement Considerations

Because a mortise and tenon joint often crosses grain direction (a rail's long grain meeting a leg's long grain running perpendicular), seasonal wood movement can stress the joint over time in wide panels. See the Wood Movement Estimator for how much a given species and board width can be expected to move.