Dovetail Layout Calculator

In short Laying out dovetails is arithmetic, and getting it wrong shows on the finished joint forever. This works out where every tail and pin falls across the width of a board, with a half-pin at each end. The half-pins are not a style choice: a full pin at the edge leaves short grain that breaks away, which is why the convention exists. Give it the board width, how many tails you want and how wide the pins should be, and it returns the position of every tail measured from one edge. Measuring cumulatively from a single edge, rather than stepping from one tail to the next, is the point — stepping accumulates error, and by the last tail a tenth of a millimetre per step has become something you can see. The tool sums every width back to the board width on each run, because a layout that does not close is a layout that will not fit, and that check is cheap. One thing this does not decide is the slope. The familiar 1:6 and 1:8 ratios describe the angle of each tail, not where it sits, and they are set by your dovetail marker or gauge. Spacing and angle are independent choices: this page handles the first and leaves the second to you.