The total pressure drop in a Stirling engine is calculated by summing the pressure drops at the hot and cold ends of the engine. The pressure drop at the hot end occurs as the working fluid expands due to heat absorption, while at the cold end, it happens as the fluid contracts and cools. Maintaining an appropriate pressure difference between the hot and cold ends is crucial for efficient engine operation. Calculating the total pressure drop requires considering factors such as temperature, volume of the working fluid, and engine design specifics.