Basically, extended length with out the shock and compressed length.....from shock mount to shock mount! Also when you have it extended would like to know what your 2.5" kings are extended to?
Prob easiest to jack one side up and ubolt the shock at the bottom....let the pack drop out and see if the shock has extra length or if the leafs do? On the other side measure from frame to bump and subtract that from the length to get a rough idea of compression. The shock compress' at an angle so it wont be exact but I can atleast compare to mine.
Mine compress to 17" mount to mount (see pic) and the leafs ext to 25.5" while the shock extends to 27" of droop....hoping it will break in more!