Dowel Spacing Calculator — Edge Joint Dowels

The dowel diameter should be no more than half the board thickness. For 18mm stock, use 8mm dowels. For 25mm stock, 10mm or 12mm dowels work well. For 12mm stock, use 6mm dowels.

Space dowels 75–150mm apart for edge joints. For structural joints, closer spacing (75–100mm) is better. For panel alignment, 150mm is adequate since the glue provides most of the strength.

Each hole should be half the dowel length plus 1–2mm clearance for excess glue. If using a 30mm-long dowel, drill each hole about 17mm deep (half the 30mm length, plus glue clearance). Never drill so deep that you risk breaking through.

Technically, a properly glued edge joint in solid wood is stronger than the wood itself. Dowels primarily help with alignment during glue-up rather than adding strength. Many woodworkers prefer biscuits or dominos for alignment.