This is the doorway where we use a PENCIL to mark the kid's height. This is also the doorway that my son thought he would decorate with a red sharpie because obviously it is an okay place to write. This is what I created and stuck on the wall to cover the mess!
Buy a board and cut it or have it cut to desired length.
Paint the board. I spray painted mine.
Use a tape measure/ruler to create the measurements on your board.
I used a Cricut to cut out vinyl numbers/lines to stick to my board.You could use a sharpie, paint, stencils, whatever.
Hang! (Shh! I hot glued my board to the wall. Glue usually peels right off when your finished.)