To properly measure shock length, you will need to completely flex your suspension. Ideally, you'll want to fully droop your front left corner, and completely compress the rear right corner. An RTI ramp is helpful, but some decent terrain will work just as well. When the vehicle is stable and it is safe to reach under the vehicle, measure the maximum and minimum length of the shocks. Then reverse the flex to check the other side. Note if any shocks are maxed out in either compression or rebound (droop). If so, remove the shock and measure from mount to mount. Then use the charts most manufacturers have online to determine which shocks will really fit your 4x4.