Joinery math

Dovetail spacing calculator with visual layout

Laid-out dovetails are equal parts geometry and taste. Too many pins and the joint looks cramped; too few and the half-pins run fat. Dead On does the arithmetic so you can focus on the feel of the piece.

The formula

tail_spacing = (board_width − half_pin_width × 2) / num_tails

Most hand-cut dovetails use a pin-to-tail ratio between 1:3 (strong, traditional) and 1:5 (fine, London-style). Whichever you pick, the half-pins at each end should match the narrow end of a full pin so the eye reads a continuous rhythm.

Example: 4 tails on a 6" drawer side

Six-inch board, 4 tails, 3 full pins, 1:5 pin-to-tail ratio. With 1/4" half-pins at each edge, the layout gives roughly 1-3/8" tail centers and 3/16" pin widths at the narrow end. Dead On draws the layout to scale so you can check the proportions before marking.

Why it matters

You can eyeball dovetails on a 4-inch drawer side. You can’t on a 14-inch blanket chest — the spacing either needs to be perfectly even or intentionally graduated, and both require math. A visual calculator lets you iterate in seconds and commit once.

Step-by-step

  1. 1

    Set board width

    The widest dimension perpendicular to the joint line.

  2. 2

    Choose number of tails

    Start with an odd number for visual balance; 3, 5, 7 are classic.

  3. 3

    Pick pin-to-tail ratio

    1:3 for strength, 1:5 for London-style refinement, 1:8 for show-off work.

  4. 4

    Set half-pin width

    Usually matches the narrow end of your pins, 3/16 to 3/8".

  5. 5

    Transfer to stock

    Use the Dead On diagram as a reference and mark from a reliable edge.

Skip the math. Build the diagram.

Dead On does the dovetail calculator and 12 other woodworking calculators with visual diagrams, offline, on every Apple device signed into your Apple ID.

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Frequently asked questions

What pin-to-tail ratio should I use?

1:3 is strongest and traditional in American work. 1:8 is the classic London pattern, finer and more decorative. 1:5 is a reasonable middle ground for most furniture.

Should the half-pins match the full pins?

Visually, yes — the half-pins at each edge should look like the narrow end of a full pin cut in half. That keeps the rhythm consistent across the joint.

Does Dead On draw the dovetail layout?

Yes. The Pro version renders the joint to scale with all dimensions labeled, so you can sanity-check proportions before you cut.

How do I mark from the calculator?

Pick one edge as your datum, transfer the tail centers from the Dead On layout using dividers or a ruler, and mark with a sharp knife rather than a pencil.

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