How do I figure out what size lift is on my Wrangler JKU?

Mine was lifted when I bought it as well. Luckily for me, there was a tag on the springs that had the part number. Check for something similar to what mine looks like.

and/or take some pictures and post them here. Someone will likly recognize it.

My JKU came already lifted with 35's. The lift is Rough Country and rides like shit. The dealership didnt know what size it is and there are no identifying numbers on it. I found this diagram online but when I measure I get anywhere between 2.75 and 3.5 depending on which tire and which driveway I use. I figure the difference may be the springs sagging? I don't know.

As others have said, check the coil spring tags if there is any. if there isn't any tags, then research the shock numbers. typically shock numbers will say they can be used for 0''-2'' or 2''-4'' lifts etc. Check for any added components like coil spring isolaters or added front or rear track bar mounts. Another way to have people here offer support is to take a shot of the system. Often others looking at your picture can identify the brand of lift based on the installed components.