This show the results of an experiment where various known forces are applied to a rubber band of unstretched length 5.56 cm and its stretched length is measured.  Second column is force in dynes x 10,000.  First column is length in cm.

Data from "A general physics laboratory investigation of the thermodynamics of a rubber band" by G. Savarino and M. R. Fisch, The American Journal of Physics, vol 59, 1991, pages 141--145, figure 2.