1) Stand with your back against a wall and separate your feet so they are shoulder width apart.
2) Place a book between your legs and against the wall with the spine of the book facing upward. Raise the book until it fits snug against your groin.
3) If you can recruit some help, have the other person measure from the top of the book (spine) to the floor. If you are on your own, use care to hold the book in place and measure from the top of the book to the floor.