Fourteen dimethyldialkoxysilanes are prepared by reacting dimethyldichlorosilane with corresponding alcohols in the liquid phase. Their physicochemical properties are determined by standard methods and their tentative empirical formulae are elucidated. The thermal conductivity values of dimethyldialkoxysilanes are determined using a two slab guarded hot plate apparatus over a temperature range of 30–190°C. The thermal conductivity values of dimethyldialkoxysilanes calculated from empirical equations are found to vary from ‐14% to +19%. Because thermal conductivity is an important parameter in heat transfer calculations, and to minimise the deviation of the values, new equations involving easily measurable ultrasonic parameters have been formulated. The proposed equations have been tested for the series of dimethyldialkoxysilanes, tetraalkoxysilanes and polydimethylsiloxanes. The thermal conductivity values computed from the proposed equations are comparable with experimental thermal conductivity values. Further, an equation involving the calculation of thermal conductivity values at varying temperatures is also proposed.