The present electron diffraction study of the molecular structure of tetramethylsilane, augmented with theoretical calculations, answers the need for accurate and detailed information on the most fundamental molecules containing silicon. The Si―C bond length is rg = 1.877 ± 0.004 Å, in perfect agreement with a previous study (Beagley, B.; Monaghan, J. J.; Hewitt, T. G. J. Mol. Struct.1971,8, 401). The C―H bond length is rg _ 1.110 ± 0.003 Å and the Si―C―H angle is 111.0 ± 0.2°. The experimental data are consistent with a model of Td symmetry and staggered methyl conformation. The barrier to methyl rotation is estimated to be 5.7 ± 2.0 kJ mol−1 on the basis of the experimentally observed average torsion of the methyl groups.