Dowel Joint Size Calculator

A well-sized dowel joint is strong and, more usefully, self-aligning. An undersized dowel adds almost no mechanical support; an oversized one splits the stock when the wood swells around the glue.

The standard rule: dowel diameter should be one-third to one-half the thickness of the thinnest piece, and in practice you take the largest standard size that does not exceed half.

For 3/4-inch stock, the usual cabinet material, that is a 3/8-inch dowel: exactly half the thickness, leaving 3/16 inch of wood on each side.
For 1/2-inch stock such as drawer sides, drop to 1/4 inch.

Hole depth per side should be at least 2.5 times the diameter, but in practice the dowel length decides it for you, since almost everyone buys pre-cut 1.5 or 2 inch dowels.

For a 1.5-inch dowel, each hole is 13/16 inch deep: half the dowel is 3/4 inch, plus 1/16 inch of glue clearance at the bottom.
That clearance is not optional. Without it the dowel bottoms out in the hole before the shoulders meet, and you end up clamping hard on a joint that has a visible line in it.

Spacing along a joint:

• Start 2 to 3 inches from each end
• Space additional dowels every 8 to 12 inches for panel glue-ups
• Closer spacing (every 5 to 6 inches) for joints that will carry shear loads

Fluted or spiral-groove dowels are preferred over smooth ones, because the grooves let glue and trapped air escape so the joint can close fully.
Plain-shank dowels can trap enough hydraulic pressure to pop the joint apart before the glue sets.