Tissue optical properties can be determined with optical coherence tomography (OCT) by fitting a model to the OCT signal. Using calibrated samples in the fixed focus geometry, the validity of the single-scattering and multiple-scattering models for both highly scattering and weakly scattering media (scattering coefficients ${\mu }_s$ ranging from 1.25 to $25.11{\mathrm{mm}}^{-1}$ ) has been investigated. The results show that, with a proper correction for the confocal properties of the sample arm, both models are appropriate to extract the scattering coefficients of weakly scattering media. For highly scattering media, the multiple scattering should be taken into account, and the multiple-scattering model can provide higher accuracy. Finally, the scattering properties of in vitro rat liver and in vivo human skin are determined. The results are useful for quantitatively characterizing tissue scattering in biomedical research and clinical diagnosis.