Diffuse phase transitions were observed in the solid solution (PbxBa1-x)TiO3. By measuring the diffuseness of the paraelectric to ferroelectric transition as a function of composition in the solid solution (PbxBa1-x)TiO3 the average size of the ferroelectric nuclei may be determined. Dielectric constant versus temperature curves were measured over the temperature range where the ferroelectric transition occurs. From these curves, the diffuseness of the transition was determined. The size of the microregions (Kanzig regions), which are responsible for the diffuse behaviour, was estimated to be between 2.5 and 4.0 nm. These microregions are the ferroelectric nuclei and hence this allows the measurement of the ferroelectric nuclei size.