The correct measurement of your shocks is important to allow full flex and reduce damage to the shocks.
In order to get the proper lengths it is vital that you flex the vehicle to maximum articulation, which may require the removal of the factory shocks.
The picture below gives an indication of what is needed to get a correct measurement.
If you do not have access to a ramp as in the picture you can also use any incline that allows you to reach maximum articulation.
There are two different types of mountings on shocks.
The first type is eye mount.
All eye type shock ends are measured from the centre of the eye where the bolt would normally go.
The second type is a pin mount.
These are measured from the base of the pin where it is fixed to the shock body.
To get the optimum shock for your vehicle we need open and closed height.
If you use a shock that is to short it will top out and may damage the top seal causing leaking.
And if a shock that is too long is used, it will bottom out and damage the valving reducing the effectiveness of the shock.