Dovetail Calculator — Pin and Tail Spacing

Use 1:6 (about 9.5°) for softwoods like pine, which need a steeper angle to prevent the short grain from breaking. Use 1:8 (about 7.1°) for hardwoods like oak and walnut. 1:7 is a good general-purpose ratio that works well with most timbers.

A common rule of thumb is that tails should be about twice the width of the pins, with half-pins at each edge about half the pin width. This gives an attractive, traditional look. Some woodworkers prefer equal pins and tails for a different aesthetic.

Half-pins are the small triangular pieces at the top and bottom edges of the pin board. They prevent the joint from sliding apart at the edges. Despite the name, they are typically about half the width of a full pin.

The depth of the dovetail (also called the length of the tail) should equal the thickness of the mating board. If joining a 20mm thick board, the tails should be 20mm long. The baseline is scribed at exactly the board thickness.

This is one of woodworking's great debates. The "tails first" method is traditional in the UK and allows you to use the tails as a template to mark the pins. "Pins first" is common in the US. Both methods produce excellent joints when done carefully.