A stock Jeep will have about 18" from the ground to the bottom of the rocker panel (botom of tub below door). Take into account the tire size and you will know about how much lift you have. i.e. A jeep with a 2" lift spring, 1" lift shackles, and 31" tires (stock tires would be 28") makes 4.5" of lift to the rocker, around 22.5" to the bottom. The stock shackles are about 4" from bolt centers, a 1" drop shackle will be around 2" longer. If you have a body lift you will see the gap between the body and frame and you will see the pucks on the body mounts. The only issue in your using this method could be old sagging springs... But this will get you close.
A few FACTS:
Rectangle headlights ARE kinda cool.
YJ does NOT stand for "Yuppie Jeep".
Jeeps should only have TWO doors.
You should ALWAYS wave at other JEEP drivers.