How to use the dovetail calculator
- Choose the number of equal tails and measure the board width.
- Specify full-pin and outer half-pin widths at the same baseline.
- Mark the returned centers, then draw the chosen slope and check the layout against the thickness and joint depth.
The formula
Tail width = (board width − 2 × half-pin width − (tail count − 1) × full-pin width) ÷ tail count
Worked example
A 150 mm board with four tails, 5 mm full pins, and 5 mm half-pins gives 31.25 mm tails at the baseline and a 36.25 mm pitch.
Before you measure and cut
Half-pin is the traditional name for the outer pin; its entered width does not have to be half the full-pin width.
This tool is a spacing aid. It does not determine joint strength, router-bit clearance, or whether angled boundaries collide at the end of thick stock.
Frequently asked questions
What does a 1:6 ratio mean?
The line moves one unit sideways for six units along the joint depth. Its angle from the depth direction is arctan(1/6), about 9.46°.
Can I use unequal tails?
This calculator divides the baseline into equal tails. An asymmetric pattern needs a custom layout.