Rare-earth orthoferrites, RFeO₃, and rare-earth iron garnets (RIGs) R₃Fe₅O₁₂ (R = rare-earth elements) were prepared by citrate–nitrate gel combustion method and characterized by X-ray diffraction method. Isobaric molar heat capacities of these oxides were determined by using differential scanning calorimetry from 130 to 860 K. Order–disorder transition temperatures were determined from the heat capacity measurements. The Néel temperatures (T_N) due to antiferromagentic to  paramagnetic transitions in orthoferrites and the Curie temperatures (T_C) due to ferrimagnetic to paramagnetic transitions in garnets were determined from the heat capacity data. Both T_N and T_C systematically decrease with increasing atomic number of R across the series. Lattice, electronic and magnetic contributions to the total heat capacity were calculated. Debye temperatures as a function of absolute temperature were calculated for these compounds. Thermodynamic functions like Cº_p,m, S^o_m, H^o, G^o, (H^o_T - H^o_298.15K), -(G^o_T - H^o_{298:15 K})/T, D_fH^o_m, and D_fG^o_m have been generated for the compounds RFeO₃(s) and R₃Fe₅O₁₂(s) based on the experimental data obtained in this study and the available data in the literature.