The orientation of the chemical shielding anisotropy tensor of the carbonate carbon in diphenyl carbonate was determined by using solid state NMR spectroscopy. The same tensor orientation was obtained from quantum mechanical calculation based on density functional theory. The most shielded direction of the tensor is along the C=O double bond. The least shielded direction is for the carbonate plane perpendicular to the C=O double bond. Chemical shielding calculations in diphenyl carbonate fragments with different conformations show that the tensor orientation measured in crystalline diphenyl carbonate also applies to the carbonate groups of bisphenol A polycarbonate. However, this orientation is not identical to that assumed so far in the work on bisphenol A polycarbonate. The consequences of this incorrect assumption in previous studies are examined.