Dowel Joint Calculator

Calculate dowel diameter, hole depth, dowel length, and spacing for edge and face joints.

Determines max dowel diameter
Length of the glued edge
Inches between dowels (6–8″ is typical)

Dowel size

Dowel diameter3/8"Largest standard ≤ ½ board thickness
Hole depth (each side)3/4"1.5× diameter, min 3/4″
Dowel length1 5/8"2 × hole depth + 1/8″ gap

Hole positions

Number of dowels3Along the joint
Actual spacing8"Evenly distributed
Centre from edge3/8"Half board thickness

Use a dowelling jig or self-centering bit to keep holes perpendicular. Drill holes slightly deeper than calculated to prevent the dowel bottoming out before the joint closes. Fluted dowels distribute glue better than smooth ones.

Standard dowel sizes

DiameterMin board thicknessTypical hole depth
1/4"1/2"3/4" each side
5/16"5/8"3/4" each side
3/8"3/4"3/4" each side
1/2"1"3/4" each side

Dowel sizing rules

Dowel diameter should be no more than half the board thickness — drilling a hole larger than this weakens the board significantly. Standard sizes are ¼″, 5/16″, ⅜″, and ½″; choose the largest that fits.

Hole depth per side is 1½× the diameter, giving enough glue surface and mechanical interlocking. Drill holes slightly deeper than the dowel half-length so the joint can close fully — trapped air and excess glue will compress against the bottom of the hole rather than splitting the joint open.

  • Use fluted or spiral dowels — glue channels prevent hydraulic lock.
  • A self-centering dowelling jig keeps holes perfectly perpendicular and aligned.
  • Space dowels 6–8″ apart for edge glue-ups; at least 2 dowels for any face joint.