Dowels come in a large variety of widths which may be measured in metric (millimetres) or imperial (inches) units. Dowel pegs sizes are usually listed in millimetres, but dowel rods may be listed either in millimetres or inches.
Dowel rods usually come in widths between 3.175mm (1/8″) and 50.8mm (2″), but they can be as wide as 304.8mm (12″).
They are usually between 304.8mm (12″) and 2.4m (9431/64) long.