Excitonic parameters of ZnO have been determined from 5 to 300 K using the combination of time-integrated four-wave mixing, continuous wave reflectivity, autocorrelation of reflectivity at the femtosecond scale, and photoluminescence spectroscopy. These techniques allow an accurate determination of both inhomogeneous and homogeneous linewidths, oscillator strength, and other parameters characteristic for excitonic resonances. It turns out that, due to impurity-exciton scattering, the homogeneous damping of A and B excitons (0.55 and 1.35 meV, respectively) predominates over inhomogeneous one in high-quality ZnO at low temperature. Our data also prove that the strong exciton-phonon coupling enhances the excitonic broadening at room temperature up to 47 meV. This approach, which combines various sophisticated spectroscopy experiments, can be employed for an accurate determination of excitonic parameters in other semiconductor compounds and in any system where excitons are confined.