Dovetail Spacing Calculator: Even Tails and Pins

The dovetail joint is one of woodworking’s most iconic joints — strong, beautiful, and resistant to being pulled apart. The interlocking tails and pins create mechanical strength that needs no glue to hold, though glue is always added for permanence.

Layout begins with the baseline — a line scribed across the board at the depth of the joint, equal to the thickness of the mating board plus 1/32 inch. Everything above this line is the joint; everything below is the shoulder.

The ratio (also called the angle) describes how steep the sides of the tails are. Common ratios:

• 1:6 (≈ 9.5°): for softwoods, steeper angle provides more mechanical resistance to the lower shear strength of pine, cedar, etc.
• 1:8 (≈ 7.1°): for hardwoods, shallower angle looks elegant and is sufficient for stronger wood

The spacing formula divides the board width into equal sections. For N tails, you create N+1 spaces, with the half-pins at each edge (half the width of a full pin space). The tail-to-pin width ratio is usually 2:1 to 3:1 — tails are wider than pins.

Example: A 6-inch wide board with 4 tails:

• Total sections = 4 tails + 2 half-pins + 3 full pins = variable
• Common approach: divide width by (2N + 1) to get unit size, where tails = 2 units wide and pins = 1 unit wide

This calculator uses the common proportional method. Lay out on the face of the board, mark with a marking gauge, then use a sliding bevel set to your chosen ratio to mark the angles.