Heat capacity of the single crystalline Er_xY_3-xAl₅O₁₂ (x = 0, 0.6, 1.1, 3), Er₂HoAl₅O₁₂, and Ho_1.5Y_1.5Al₅O₁₂ garnets was measured in the temperature range from 1.9 to 220 K at zero magnetic field and at fields up to 9 T. The Schottky anomalies were found for the garnets with magnetic ions. The heat capacity was fitted by a sum of the Debye, Einstein, and Schottky contributions. The entropy and magnetic entropy were evaluated. The magnetic entropy magnitude in the garnets with erbium ions suggests the application of these garnets in adiabatic demagnetization refrigerators.