The dovetail is prized for one reason: its angled tails mechanically lock into the pins so the joint cannot pull apart in the direction it is loaded. Getting that lock right starts with a consistent slope angle and an even, deliberate layout, both of which this calculator produces from a couple of numbers.
How it works
Dovetail slope is traditionally written as a ratio of 1 to N, meaning one unit of rise for every N units of run. Converting that to an angle you can set on a bevel gauge is a single trigonometric step.
angle = atan(1 / N) degrees from vertical
offset = thickness / N how far the line travels across the faceA 1 to 6 ratio gives about 9.46 degrees and a 1 to 8 ratio about 7.13 degrees. For layout, the tool places a half-pin at each edge, then divides the remaining width into equal tails separated by interior pins, and draws the result to scale so you can mark straight from it.
Worked example
Suppose a 150 mm wide, 18 mm thick pine drawer side with three tails at a 1 to 6 slope and 6 mm half-pins.
- Bevel angle: atan(1/6) ≈ 9.46 degrees
- Face offset (how far the slope travels across the 18 mm thickness): 18 / 6 = 3 mm
- Usable width (after removing two half-pins): 150 − (2 × 6) = 138 mm
- Each tail + pin cycle: 138 / 3 cycles = 46 mm; with the tail wider than its adjacent pin, roughly 28 mm tail and 18 mm pin
The result: three 28 mm tails separated by two 18 mm interior pins, with a 6 mm half-pin at each edge. The scaled SVG diagram reflects this layout for direct marking.
Setting up the cut
Set the calculated angle on a sliding bevel gauge or a dedicated dovetail marker. Scribe the baseline shoulder line around all four faces of the tail board at a depth equal to the receiving board’s thickness — this is the depth to which your saw cuts. Transfer the tail spacing from the diagram with a marking gauge and sharp knife before reaching for the saw.
The golden rule of hand-cut dovetails: cut the tails first, then use them as a template to scribe the pins. Clamping the tail board over the pin board and running a sharp knife inside each tail socket eliminates layout error at the most critical point.
Ratio and material guidance
| Material | Typical ratio | Approximate angle |
|---|---|---|
| Softwood (pine, cedar) | 1:6 | 9.5° |
| Hardwood (oak, walnut) | 1:8 | 7.1° |
| Hardwood (fine detail work) | 1:10 | 5.7° |
Steeper angles (lower N) resist pull-apart better in weak fibres but can look crude. Shallower angles suit dense hardwoods that need less mechanical help and reward precise fitting. Both hold reliably when fitted well — preference and aesthetics drive the choice as much as engineering does.
Common mistakes to avoid
- Baseline too shallow: if the baseline is set at less than the full receiving board thickness, the joint will gap on the show face.
- Half-pins too thin: less than about 5 mm on the edge is fragile; the short grain runs straight into the slope and splits when the joint is driven home.
- Marking with a pencil: pencil lines are 0.5 mm wide, which is half the tolerance in a well-fitted joint. Use a marking knife or a hard mechanical pencil.
- Sawing to the wrong side of the line: saw just inside the waste — the pins sit in the spaces between the tails, and any wood you leave there will prevent the joint closing.