Dovetail Joint Calculator

The engine estimates the tail count by assuming a tail width roughly twice the pin width, which mirrors a common visual proportion in hand-cut dovetails where the wider tails read as the dominant decorative element and the narrower pins look delicate between them. It's purely an aesthetic starting point built into the estimate, not a structural requirement — you can still get a strong joint with a different tail-to-pin ratio, the calculator just uses 2:1 to pick a sensible initial tail count before solving the exact widths.

This layout treats the two edges of the board as half-pins, which are entered separately and already bookend the joint on both sides. Between N tails there are only N-1 full pins, since a full pin only exists in the gap between two adjacent tails — the outermost gaps are filled by the half-pins instead, which is why pinCount is calculated as tailCount minus 1.

It converts your dovetail angle in degrees into the traditional woodworking shorthand of "1 in X," calculated as 1 divided by the tangent of the angle — a 14° angle comes out to roughly 1:4 and 8° to roughly 1:7. Many woodworkers set a sliding bevel or dovetail marking gauge using that ratio rather than a protractor, so this conversion lets you transfer the calculator's angle directly onto your layout tool.

It returns zeros whenever the available width after removing both half-pins is zero or negative, or when the pin width itself is zero or negative — both indicate the board is too narrow for the half-pin size you specified, or the pin width value doesn't make physical sense. Increase the board width, reduce the half-pin width, or enter a positive pin width to get a real layout instead of the zeroed-out fallback.