How to use the dovetail layout calculator
- Choose inches or millimeters and enter the board width, the number of tails and the board thickness.
- Set the pin width compared with a tail. A value of 0.5 makes each pin half as wide as a tail, measured at the end of the board.
- Set the slope: 6 means 1:6, and 8 means 1:8. The defaults are only examples.
- Mark the tail edges on the end of the tail board from the table, then draw the sloped sides to the baseline marks.
Formula
board width W = n x (t + p), with p = ratio x t
t = W / (n x (1 + ratio)) and half pin = p / 2
side movement = thickness / slope
tail at the baseline = t - 2 x thickness / slope
The layout has n tails, n - 1 full pins between them and a half pin at each edge. All widths at the end are measured along the end of the tail board. A slope of 1:6 corresponds to an angle of about 9.46 degrees, and 1:8 to 7.13 degrees.
Three tails across a 6-inch board
For a 6 inch board, 3 tails, a pin ratio of 0.5, a thickness of 0.75 inch and a slope of 1:6, each tail is 1.3333 inches wide at the end, each pin 0.6667 and each edge half pin 0.3333. Together 3 x 1.3333 + 2 x 0.6667 + 2 x 0.3333 = 6 inches.
The side moves 0.75 / 6 = 0.125 inch over the depth of the joint, so a tail is 1.0833 wide at the baseline and the gap between tails is 0.9167. The first tail spans 0.3333 to 1.6667 at the end and 0.4583 to 1.5417 at the baseline; the layout is mirror symmetric across the board.
Setting up the joint
Hand-cut dovetails are laid out by marking the tails on one board, cutting them, and scribing the pins from them. The positions above are for the tail board. Many woodworkers start and end with a half pin so the joint looks balanced and the edge has support, but that is a style choice.
A steeper slope looks more decorative and grips better against pulling, but the thin points of the tails are fragile in softwood; a gentler slope is stronger and easier to cut. If the slope would make the tails shrink to nothing at the baseline, the page says so and asks for a gentler slope or fewer tails.
Layout and tools
Allow the saw kerf and a little paring when you transfer the marks. For other joinery layouts, the Box Joint Finger Calculator spaces straight fingers, the Miter Angle Calculator gives cutting angles and the Cut List Optimizer plans boards for your parts.
More layout tools
For other layouts and cutting sizes, try the Flying Geese Cutting Calculator, Quarter Square Triangle Calculator and Pillow Cover Size Calculator.
Assumptions and limits
- The joint is a through dovetail with a half pin at each edge, and widths are measured at the end of the tail board.
- The slope is the same on every tail, and the thickness is the depth of the joint.
- Pin width at the end is the ratio times the tail width at the end.
- The marks are a layout; saw kerf, paring and wood movement are for you to allow.
Frequently asked questions
What do 1:6 and 1:8 mean?
They describe how far the side moves sideways for each unit of depth: 1 unit in 6, or 1 in 8. The angles are about 9.46 and 7.13 degrees. Which one to use is a matter of preference and the wood.
Why is the pin narrow at the end and wide at the baseline?
The tails flare outward toward the end of the board, so the gaps between them are narrow at the end and wider at the baseline. The table gives both sets of marks.
How many tails should I use?
More tails make a finer joint and need more cutting. For a given width the choice is mostly looks. Try a few values; the table updates at once.
Do I need a half pin at the edge?
It is a common convention, not a rule. If you prefer a full-width pin or none at the edge, adjust the layout by hand from the tail positions shown.