In this study, we investigated the sodium site occupancies in the Na x Fe[Fe(CN) 6 ] Prussian Blue framework as the sodium composition (0 ≤ x ≤ 2) is varied. This is achieved by a convex hull scheme based on density functional theory (DFT). We study the relevant sodium site occupancies and magnetization as a function of sodium concentration. Our theoretical investigation reveals the tetragonal Na/vacancy ordering in the thermodynamically stable Na 1 Fe[Fe(CN) 6 ]) phase, a feature previously reported in the literature. Furthermore, as recent studies have confirmed, the rhombohedral distorted phase is more stable than the cubic one for higher concentrations of sodium. Notably, this is the first time that the compositional phase diagram of a Prussian Blue electrode has been derived from first principles for all 24 of the 24d sites. Our results provide valuable insights into the complexities of sodium (de)insertion in Na x Fe[Fe(CN) 6 ]) electrodes, which are crucial for the further improvement of high-rate capacity Prussian Blue electrodes.