I am making my first mortise and tenon joints.  Yea for me.  I am using a mortising machine to make to mortises. (makes sense) I am using 2×4’s to practice.  I do have a jointer so they will be flat and square.  My question is this.  If I use 1.25 inch square rails how wide should the tenon be? Also how long should they be?  I have so far ripped 2×4’s to 2″ and then glued them to another full size 2×4 to make an L shap.  So the L shape is 3.5 inches on each side.  I am just making some simple shelves for a beasement utility room.  I figured I would practice on some cheap wood first. 

My thought would be to make the tenons 3/8 to 7/16 wide.   3/8 is a little lest than a third of the width of the tenon and 7/16 is a little bigger than a 1/3 of the width.  And I would think an inch or inch 1/2 long would be fine too.  Any thoughts

thanks,

Kenney66