Joinery Calculators

Calculators for dovetails, mortise and tenon, box joints, dowels, dados, and miter angles - get the exact dimensions before you cut.

Biscuit Joint CalculatorBiscuit Joint Calculator for edge, T and miter joints. It picks #0, #10, #20 or FF, sets slot spacing and…Box Joint CalculatorBox Joint Calculator that splits a board into equal fingers and gives the jig setting, cut depth, glue area and…Bridle Joint CalculatorBridle Joint Calculator sizing the slot and tenon at one-third of the stock, with blade heights, the tenon jig setting,…Dovetail CalculatorDovetail Calculator giving tail and pin widths at the end and baseline, slope offsets, gauge settings, half-blind laps and sliding…Dovetail Spacing CalculatorDovetail Spacing Calculator finding the divider step, pin centers from both edges and a tilted-rule layout, with graduated tails and…Dowel Spacing CalculatorDowel Spacing Calculator that lists each hole center from both ends, even or tight at the ends, with hole depth,…Lap Joint CalculatorLap Joint Calculator that finds half-lap cut depth and shoulder marks for cross, T, corner and splice joints, plus dado…Mortise and Tenon CalculatorMortise and Tenon Calculator that sizes a tenon off the leg or stile it fits into, with its length, the…Pocket Hole CalculatorPocket Hole Calculator that picks a Kreg screw off the thinner of the two boards and your jig, sets its…Polygon Angle CalculatorPolygon Angle Calculator that finds the interior and exterior angles for any side count, then sets the miter or bevel…Spline Joint CalculatorSpline Joint Calculator that sets the groove and the spline to rip for a wood edge joint, a hidden spline…Tongue and Groove CalculatorTongue and Groove Calculator that counts the boards to fit a wall, ceiling or full room by face width, with…

Woodworking Joint Calculators

A joint is only as good as its proportions. Size it wrong and it racks loose, splits the stock, or fails under load. These calculators give you the dimensions and angles that make a joint hold - before you cut into good material.

Mortise and tenon

The mortise and tenon is the backbone of frame and furniture work. Strength comes from proportion, and the standard is the one-third rule: the tenon thickness is one-third of the stock thickness. A 3/4-inch rail gets a 1/4-inch tenon; a 1-1/2-inch timber gets a 1/2-inch tenon. That leaves equal walls on each side, so neither the tenon nor the mortise wall is the weak point. Our mortise and tenon calculator sizes tenon thickness, shoulders, width, and depth from your stock - through, blind, or haunched.

Dovetails

Dovetails are judged on spacing and slope. The traditional slope is 1:6 for softwoods and 1:8 for hardwoods, roughly a 7 to 10 degree angle. Too steep and the tails weaken; too shallow and the joint can slip apart. Our dovetail calculator spaces pins and tails evenly across the board and sets the half-pins at each edge, so the layout is balanced before you mark a line.

Box joints, dowels, and dados

Box joints need even fingers that match your blade kerf, or the last finger comes out a different width. Dowels need consistent spacing and setback to pull an edge joint tight. Dados should match the real thickness of your plywood, which is almost never a full 3/4 inch. Each calculator here works from your actual material, in inches or millimeters, so the layout fits the wood in front of you.

These proportions are proven starting points, not fixed law - adjust for very soft or very dense species, and always test the fit on a scrap of the same stock before committing to the real joint.