Enter your stock dimensions and joint type — get correctly proportioned tenon thickness, length, shoulder width, and mortise depth, plus a live diagram. Based on the classic ⅓ rule and furniture-maker proportions.
Step 1
Stock dimensions
Step 2
Joint type
Tenon Dimensions
Thickness—
Nearest chisel
Width—
Length—
Face shoulders—
Edge shoulders—
Haunch depth—
Mortise Dimensions
Width—
Length—
Depth—
Min. back wall—
Joint Diagram
The ⅓ Rule
Tenon thickness should be ⅓ of the rail's finished thickness. This balances glue area with remaining wood strength on both the tenon cheeks and the mortise walls.
Grain matters
Long-grain to long-grain glue joints (tenon cheeks to mortise walls) are very strong. Short-grain shoulders carry little load — they're for alignment and appearance. Don't rely on them for strength.
Fit before glue
A well-fitted tenon should slide in with hand pressure and hold its own weight when vertical. Too tight stresses the joint. Too loose and there's nothing for the glue to bridge.