Dovetails carry a certain reputation. They’re the joint people point to as the mark of real furniture making, which makes them slightly intimidating to approach for the first time — and the layout maths, done by hand, doesn’t help.
The cutting is a skill that takes practice. The layout, though, is arithmetic, and there’s no particular virtue in doing it on the back of an envelope. This tool handles that part so you can spend your attention on the sawing.
Enter your board width, material thickness, and the joint you want, and it returns the exact tail and pin widths, the cutting angle in degrees, and the spacing to mark out. It covers both through and half-blind dovetails, and shows the joint in 3D — flat, or folded to a 90° corner as it will actually be assembled.
The angle is given in degrees as well as ratio, which matters because you set a sliding bevel in degrees but talk about dovetails in ratios.
The tool opens with a through dovetail in a 150 × 20mm board, two tails, a 2:1 tail-to-pin ratio, and a 1:8 angle. That gives:
Angle: 7.13° (1:8)
Tail face: 55 mm
Tail baseline: 50 mm
Pin face: 20 mm
The two tail figures are the ones worth understanding, because the difference between them is the dovetail. The tail measures 55mm across its widest point at the face of the board, and 50mm at the baseline where it meets the shoulder. That 5mm of taper across the tail is the wedge — it’s what physically resists the joint being pulled apart, before any glue is considered.
The 2:1 ratio means each tail is twice the width of a pin at the shoulder line. Changing it to 3:1 gives you narrower pins and a finer, more traditional look; 1:1 gives pins and tails of equal width, which reads as more geometric.
The 1:6 and 1:8 convention is worth knowing, and it has real mechanical reasoning behind it rather than being pure tradition. But it’s less rigid than it’s often made to sound. Look at antique furniture and you’ll find dovetails cut anywhere from roughly 7° to 14°, and with modern PVA glue doing structural work that a hide-glue-era joint relied on the angle alone for, the split has become as much about appearance as necessity.
Where the range genuinely matters: below about 1:4 the short-grain fragility at the tail tips shows up regardless of species, and above about 1:9 the joint starts to read visually as a plain box joint rather than a dovetail. Between those, it’s closer to taste than rule — plenty of woodworkers settle on 1:7 for everything and set one bevel once.
It works like a roof pitch. A 1:6 ratio rises six units for every one unit across, giving a steeper angle of roughly 9.5°. A 1:8 rises eight for every one, a shallower 7.1°. The convention is 1:6 for softwoods and 1:8 for hardwoods, though in practice anything from about 7° to 14° holds up fine.
Softwood fibres compress relatively easily, so a steeper angle creates a stronger wedge-shaped mechanical lock before the wood gives. Hardwood resists compression on its own and doesn't need as steep a lock — and a steep angle in hardwood leaves thin, fragile short grain at the tips of the tails, which is genuinely prone to snapping during cutting or assembly.
A through dovetail is visible from both faces — the tails pass right through, showing end grain on both sides. It's the usual choice for carcase corners. A half-blind dovetail stops inside a lap so the joint is hidden from the front, which is why it's the standard for drawer fronts. The angle principle is identical for both.
There's no fixed rule, and antique furniture shows a wide range. More tails read as finer and give more glue surface; fewer read as bolder and are quicker to cut. Board width matters more than any formula — cut a test joint in your actual stock and thickness, because a spacing that looks right in a thick carcase side can look clumsy in a thin drawer side.
Yes, and it's the detail most often missed. The outermost element at each edge is a half-pin — a pin with only one angled face. It's what stops the outer tail from having a fragile, unsupported short-grain edge at the board's edge, so it's structural rather than decorative.