How can I predict the compressive load generated by squeezing an O-ring?

The force required to compress an O-ring primarily depends on the hardness of the O-ring, its cross section, and the amount of compression. Even if all these factors are the same, the compression force per-inch for two rings can still vary if the rings are made from different compounds or if their inside diameters are different. The anticipated load for a given installation is not fixed, but is a range of values. Increase in temperature softens elastomeric materials, yet the compression force decreases very little except for the hardest compounds.