Box Joint (Finger Joint) Spacing Calculator
Calculate the number of pins and spaces for a box joint given board width and desired pin size.
Get exact spacing for a perfect fit.
What Is a Box Joint? A box joint (also called a finger joint) consists of interlocking rectangular pins and spaces cut at the end of two boards. When the joints mesh, the mating pieces lock together with a large glue surface area — it is both strong and visually attractive.
The Layout Rule For a proper box joint, a board must begin and end with a pin (or begin with a space and end with a space). This means the number of pins and spaces must work out evenly. The board width should ideally be an exact multiple of the pin size.
Adjusting for Width If your board width is not a perfect multiple of the pin size, you have two options: adjust the pin size slightly so it divides evenly, or adjust the board width. Many woodworkers prefer to adjust the pin size by a small fraction — a difference of 1/64" is invisible.
Jig Setup Box joints are typically cut with a dado stack or router table using a sled jig with an indexing pin. The pin width equals the width of each cut. Accuracy in the jig setup determines whether the joint is too tight, too loose, or perfect.