The size and surface effects on the nematic‐isotropic phase transition of a liquid crystal are analyzed using a functional form of the surface energy proportional to the square of the scalar order parameter. The evaluated temperature shift agrees with the published experimental observations. This form seems confirmed by experimental data of the anchoring energy versus temperature, determined by means of the Freedericksz technique. The obtained formula for the temperature shift is similar to the well‐known Thomson formula, usually considered in the classical phase transitions.