Use this workshop calculation to turn measured dimensions and the selected construction convention into a cut, spacing, fit, or material-planning value.

Board edge width (mm)

Required number input.

Equal fingers

Required integer input.

Divide board edge width into a specified number of equal-width box-joint fingers. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Finger width (mm)

The resulting finger width returned as a number.

• Nominal dimensions, kerf, moisture movement, hardware clearances, wall squareness, and manufacturer instructions can change the required shop dimension. Measure the actual assembly and test critical joints on scrap before cutting finished material.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Complement the calculated dimension with a physical story stick, dry fit, or full-size layout. Follow the hardware, coating, adhesive, or machine manufacturer's limits where they differ from a rule of thumb.

• Box Joint Depth

  Size box-joint fingers from mating board thickness plus deliberate protrusion before flushing.

• Finger Joint Count

  Choose the nearest positive integer finger count to a target finger width over a measured joint edge.

• Box Joint Pitch Calculator

  Compute an even finger joint pitch that fits a whole pin count into the joint width.