The uncertainty of thermophysical data is indispensable information when reporting both experimental and calculated values. In this paper, we present an evaluation of the uncertainty of the ideal-gas entropy and heat capacity calculations by density functional theory (DFT) for molecules containing symmetrical internal rotors. The rigid-rotor harmonic oscillator (RRHO) and one-dimensional hindered rotor (1-DHR) models are compared as well as the effect of the scale factors employed. The calculations of the standard ideal-gas entropy (S-g0) are performed for a selected set of 33 molecules for which reliable reference data were found in the literature. The RRHO model provides S-g0 with the absolute average percentage deviations (sigma(r)) about 2 % from the reference data. Scaling the frequencies does not lead to any improvement when using the RRHO model. A significant improvement is achieved when the 1-DHR model and scale factors for low and high frequencies are applied simultaneously (sigma(r) less than 0.3 %). The ideal-gas heat capacity (C-p(g0)) calculations were tested on a set of 72 molecules. The RRHO model yields C-p(g0) values with sigma(r) up to 3 % at 300 K and 1 % at 1000 K while using the 1-DHR model coupled with a pair of scale factors lowers sigma(r) to less than 1.5 % and 0.5 % at 300 K and 1000 K, respectively.