It is shown from the measured raindrop size spectra in precipita-tion of convective cloud and stratus that they can be approximated byexponential function with the intercept N₀ and slope Λ. The parame-ters N₀ and Λ are related to the mean rainfall rate diameter, whichis defined here, and the relationship between them is in good agree-ment with the theoretical expression derived. Based on the above results, a method for estimating N₀ and Λ interms of reflectivity factor and rainfall rate is suggested. The valuesof N₀ and Λ calculated by the method basically consist with thoseanalysed from real data.