Dovetail Joint Spacing Calculator
Enter your board width, tail count, and wood type to get tail width, pin width, angle, and a live layout diagram. Evenly spaced across the full board width. Nothing uploaded.
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Full measurements
Learn more: dovetail spacing and angle
How the board width is split
The calculator divides the board width by the number of tails to get one pitch, the width of a tail plus a pin. It then splits each pitch using your tail-to-pin ratio. On a 150 mm board with 5 tails and a 2.5:1 ratio, the pitch is 30 mm, each tail is 21.43 mm and each pin is 8.57 mm.
The ends are half-pins, each half the width of a full pin (4.29 mm here). With 5 tails you get 4 full pins between them plus two half-pins on the edges, and the total comes back to exactly 150 mm.
What the angle ratios mean
A ratio of 1:6 means the side of the tail moves 1 unit sideways for every 6 along its length. That is an angle of 9.46 degrees. 1:8 is 7.13 degrees and 1:10 is 5.71 degrees, so 1:6 is the steepest of the three and 1:10 the shallowest.
The presets pair 1:6 with softwood, 1:8 with hardwood and 1:10 with fine hardwood. The Custom option is fixed at 1:7, or 8.13 degrees. Treat the presets as starting points and adjust to the wood and the look you want.
Where the numbers stop
The calculator gives layout widths and the angle, and draws the tails. It does not account for the saw kerf, the thickness of your marking line or how much waste you pare away. Mark out from the numbers and test on an offcut before cutting your final boards.
FAQ
Why is there a half-pin at each edge?
The layout alternates tails and pins, so a joint with N tails has N - 1 full pins between them. The two edge half-pins together add up to one more full pin, which makes the board split into N equal pitches.
Which ratio should I pick?
The calculator suggests 1:6 for softwood, 1:8 for hardwood and 1:10 for fine hardwood. These are common starting points, not strict rules, so pick the one that suits your wood and your eye.
Can I make the tails wider or narrower?
Yes. The tail-to-pin width ratio field accepts values from 1 to 8. A ratio of 1 gives tails and pins of equal width, and a higher ratio makes the tails wider and the pins thinner.