Dovetail Joint Calculator
Calculates tail and pin spacing for hand-cut dovetail joints given board width, thickness, angle, and pin ratio. Use it before marking out joinery to get precise, evenly spaced cuts every time.
Last updated: September 2026
Formula below · 2 sources (fpl.fs.usda.gov, Wikipedia) · Updated Sep 2026
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About this calculator
This layout gives the width of each tail when a board is divided into equal tails with narrower pins between them. The dovetail slope is a ratio 1:N (for example 1:8 means the side of a tail moves 1 inch sideways for every 8 inches along the cut). Across the board thickness that slope offsets each edge by boardThickness ÷ N, which is reserved for the edge half-pins. The remaining width is shared by numberOfTails tails and numberOfTails − 1 pins, each pin being pinRatio times a tail: tailWidth = round(((boardWidth − 2 × boardThickness ÷ N) ÷ (numberOfTails + (numberOfTails − 1) × pinRatio)) × 16) ÷ 16, rounded to the nearest 1/16 inch for marking out. Pin width = pinRatio × tailWidth. A steeper slope (1:6) reserves a little more width at the edges than a shallow one (1:8 or 1:10). Treat the result as a starting layout and adjust half-pin widths to taste.
How to use
Suppose you have a 6-inch-wide board, 3/4 inch thick, and you want 4 tails at a 1:8 slope with a pin ratio of 0.4. Step 1 — edge offset: 0.75 ÷ 8 = 0.094 inch per side, 0.1875 inch for both. Step 2 — remaining width: 6 − 0.1875 = 5.8125 inches. Step 3 — divide among 4 tails and 3 pins at 0.4: 4 + 3 × 0.4 = 5.2 tail-widths. Step 4 — tail width: 5.8125 ÷ 5.2 = 1.118, rounded to 1-1/8 inches (1.125). Each pin is then about 0.4 × 1.125 = 0.45 inch wide.
Frequently asked questions
What dovetail angle should I use for hardwood vs softwood?
The conventional rule is 1:8 (approximately 7°) for hardwoods like oak or maple, and 1:6 (approximately 9.5°) for softwoods like pine or cedar. Hardwoods are denser, so a shallower angle still provides excellent mechanical lock without weakening short grain at the pin. Softwoods are more prone to short grain failure, so a steeper angle keeps the pin wider at its base. Many hand-tool woodworkers use 10° as a universal compromise that works well across species.
What is a good pin to tail ratio for traditional hand-cut dovetails?
A pinRatio of 0.3 to 0.5 is typical for furniture-grade work, meaning pins are about one-third to one-half the width of tails. Very fine hand-tool work sometimes uses ratios as low as 0.15 to create the elegant, slender pins seen in antique furniture. Wider pins (ratio above 0.6) are common in utilitarian carcass work where speed matters more than aesthetics. The ratio directly affects how many tails fit within a given board width, so experiment in the calculator before committing to a layout.
How do I convert a tail width fraction to a marking gauge setting?
The calculator rounds results to the nearest 1/16 inch, which corresponds directly to standard imperial ruler markings. To set a marking gauge, read the decimal fraction and identify the closest 1/16 graduation — for example 0.9375 inches is exactly 15/16 inches. If your result falls between two markings, trust the rounded value; small discrepancies under 1/32 inch are within hand-tool layout tolerance. Always verify your layout by drawing one full repeat on scrap before cutting the actual board.