The Stirling engine consists of two isothermal cycles and two constant volume cycles. The working principle of the Stirling Engine is to take advantage of changes in the pressure and volume of the gas in a closed system. The Schmidt method is an isothermal calculation method for the Stirling engine based on an ideal gas's isothermal expansion and compression. The method used is analytical and experimental, varying the rotation, compression, and cylinder temperature with the Hirata method. This study aimed to see the effect of air temperature expansion, compression, and temperature changes (∆T). After doing it, it can be concluded that the maximum rotation of P1 = 390 rpm, P2 = 387 rpm, and P3 = 399 rpm. The maximum torque of P1 = 0.967 N.m with a maximum power of 39.5 watts. P2 = 0.96 N.m with a maximum power of 38.9 Watts, and P3 = 0.99 N.m with a maximum power of 41.3 Watts. Calculations using the Hirata method show that the maximum temperature value in the compression cylinder (Tc) P1 = 49.7 ˚C, P2 = 51 ˚C, and P3 = 50 ˚C. Expansion cylinder (Te) P1 = 172.3 ˚C, P2 = 189.6 ˚C and P3 = 198.9 ˚C. Heater temperature (Th) P1= 576 °C, P2= 678.1°C and P3= 769.4 °C. Temperature change (∆T) P1= 126.1 °C, P2= 142.9 °C, and P3= 151 °C. The maximum pressure of the first experiment is 1.2504 Bar. In the second experiment, the maximum pressure reached 1.265 Bar. And in the third experiment, the maximum pressure is 1.2525 Bar.