In a swelling state at a temperature of incipient dissolution, an acrylic fiber is highly elastic just like a rubber. A system of entangled macromolecular chains is considered analogous to a cross-linked rubber network and from the theory of rubber elasticity, the measured extension modulus of an acrylic fiber at the terminal swelling state may be used to calculate the number of entanglements. By means of a capillary rheometer, a series of model acrylic fibers with varied degrees of entanglements were prepared. The entanglements present in these model fibers were then measured by the other two thermal methods (SDSC and SSS/SS methods) already established in our laboratory. The die swell ratios were also measured microscopically at the exit of the capillary rheometer. The experimental results of entanglements measured by the various methods were well correlated, at least qualitatively.