Gas spring force calculation is normally designated as P1 which is the force measured .2" (5 mm) from full extension in the extending direction. Force is a function of the charge pressure in the cylinder acting on the cross section of the rod. The smaller the diameter of the rod the lower the force at the same pressure. For example, a spring with a 10 mm rod charged to a pressure of 1000 psi will yield a P1 force of 118 lbs. while a spring with a 6 mm rod charged to the same pressure will yield a force of only 41 lbs.
Compressed force is referred to as P2. P2 is measured .2" (5 mm) from full compression in the extending direction and will always be greater than P1 as explained under K-Factor.