The effect of excluded volume on the coil size of dilute linear polymers was investigated by off-lattice Monte Carlo simulations. The radius of gyration R-g was evaluated for a wide range of chain lengths at several temperatures and at the athermal condition. The theta temperature and the corresponding theta chain dimensions were established for the system, and the dependence of the size expansion factor, alpha(s) = R-g/(R-g)(theta), on chain length N and temperature T was examined. For long chains and at high temperatures, alpha(s) is a function of N/N(s)double dagger alone, where the length scale N(s)double dagger depends only on T. The form of this simulations-based master function compares favorably with alpha(s)(M/M(s)double dagger), an experimental master curve for linear polymers in good solvents, where M(s)double dagger depends only on polymer-solvent system. Comparisons when N(s)double dagger(T) and M(s)double dagger(system) are reduced to common units, numbers of Kuhn steps, strongly indicate that coil expansion in even the best of good solvents is small relative to that expected for truly athermal solutions. An explanation for this behavior is proposed, based on what would appear to be an inherent difference in the equation-of-state properties for polymeric and monomeric liquids.