Dovetail and Box Joint Layout Calculator

Laying out through dovetails by hand means dividing the board into equal tails with pins of a chosen width and half pins at the edges, then carrying the angle from the end of the board to the baseline. This calculator does the arithmetic for any width, number of tails, pin width and slope, and prints the marks you need along the end and along the baseline. Switch to box joint and it finds a finger width that divides the board evenly.

Dovetail layout calculator

How it works

Tail width at the end = (board width − 2 × half pin − (tails − 1) × pin) ÷ tails, all measured on the end of the board where the pins are narrowest
Slope = thickness ÷ ratio (a 1:8 slope over 3/4 in is 3/32 in), so each tail is 2 × slope narrower at the baseline and each pin 2 × slope wider
Angle = arctan(1 ÷ ratio): 1:8 is 7.1°, 1:7 is 8.1°, 1:6 is 9.5°
Box joint: fingers = board width ÷ finger width, rounded to a whole number, and the finger width recalculated to divide the board exactly

Worked example

A 6 in wide, 3/4 in thick drawer side with four tails, 1/4 in pins, 3/8 in half pins and a 1:8 slope:

Units: Inches and feet
Joint: Through dovetail
Board width: 6 in
Board thickness: 0.75 in
Number of tails: 4
Pin width at the narrow end: 0.25 in
Half-pin width at the narrow end: 0.375 in
Dovetail angle: 1:8 (about 7.1°, hardwoods)

The calculator gives:

Tail width at the end of the board: 1-1/8" (15/16" at the baseline)
Pin width: 1/4" at the end, 7/16" at the baseline
Half pins: 3/8" at the end, 15/32" at the baseline
Dovetail angle: 1:8 = 7.1° (the sides lean 3/32" over the 3/4" thickness)
Tail spacing, centre to centre: 1-3/8"
Marks along the end of the tail board: 0, 3/8, 1-1/2, 1-3/4, 2-7/8, 3-1/8, 4-1/4, 4-1/2, 5-5/8, 6
Marks along the baseline: 0, 15/32, 1-13/32, 1-27/32, 2-25/32, 3-7/32, 4-5/32, 4-19/32, 5-17/32, 6

Each tail is 1-1/8 in at the end of the board and 15/16 in at the baseline; the pins are 1/4 in at the end and 7/16 in at the baseline. The marks along the end run 0, 3/8, 1-1/2, 1-3/4, 2-7/8, 3-1/8, 4-1/4, 4-1/2, 5-5/8, 6. Mark the end, set a bevel gauge to 7.1° and carry the lines to the baseline; the baseline marks let you check them.

Notes and limits

Set the marking gauge for the baseline to the thickness of the mating board plus a hair (1/64 in) so the joint can be planed flush.
The drawing shows the tail board. Pins on the pin board are the spaces between the tails, transferred with a knife from the cut tails.
Hardwoods take 1:8, softwoods 1:6; 1:7 is a common compromise. Steeper (1:6) is stronger in soft wood, shallower looks finer.
Very narrow pins (under 5/32 in) are delicate to chop; leave more room in softwood.
For box joints on a jig, the calculator’s adjusted finger width is the key width to cut on the jig; the pin on the jig must match it exactly.

Frequently asked questions

How do you space dovetails evenly?

Decide the pin width and half-pin width at the end of the board, subtract them from the width, and divide the rest by the number of tails. This calculator gives the marks; dividers walking across the board do the same thing.

What angle should dovetails be?

1:8 (about 7°) for hardwood and 1:6 (about 9.5°) for softwood are the traditional choices. Anything between them works; the joint is a matter of fit, not the exact angle.

How many dovetails should a drawer have?

For a 6 in drawer side, three to five tails look right. More, narrower tails look finer; fewer, wider tails are quicker and stronger in softwood.

How wide should box joint fingers be?

Commonly 1/4, 3/8 or 1/2 in, adjusted so a whole number fits the board. The calculator changes your target width to the nearest one that divides evenly.

How deep do I cut dovetails?

To the thickness of the mating board, marked with a gauge. Cutting a hair deep and planing flush is normal; cutting shallow leaves a gap.

Sources

USDA Forest Products Laboratory, Wood Handbook: Wood as an Engineering Material (FPL-GTR-282), board foot and lumber size definitions

Last reviewed: 26 September 2026. The calculation is covered by automated tests with known answers taken from the sources above. Found an error? Please let us know.