Tenon thickness: A tenon's thickness should be one-third the thickness of the stock being mortised. So, if you are joining two pieces of 3/4″material, the tenon should be ¼” thick (1/3 of ¾). If you are joining a 7/8″-thick apron to a 1-1/2″-thick table leg, the tenon should be 1/2″ thick (1/3 of 1-1/2).

How deep should I make a mortise?

The mortise depth should be roughly three times the thickness of the tenon. It can be cut in several ways, among them the traditional approach of using sturdy mortising chisels and a mallet to chisel out the hole by hand.

How long should tenons be?

Tenon length: The general rule is that the minimum tenon length is five times its thickness. So a 1/4″-thick tenon should be 1-1/4″ long.