The development of highly efficient cooling technologies has been identified as a key strategy to address the mitigation of global warming. Especially, electrocaloric materials have emerged as promising candidates for cooling applications, owing to their potential to provide high cooling capacity with low energy consumption. To advance the development of electrocaloric materials with a significant electrocaloric effect (ECE), a thorough understanding of the underlying mechanisms is required. Previous studies have estimated the maximum ECE temperature change by calculating the entropy change between two assumed states of a dipole model, assuming polarization saturation with a sufficiently large electric field. However, it is more relevant to assess the ECE under continuously changing electric fields as this is more reflective of real-world conditions. To this end, we establish a continuous transition between the complete disorder state and the polarization saturation state using the partition function to derive the entropy change. Our results demonstrate excellent agreement with experimental data, and our analysis of energy items within the partition function attributes the increase in the ECE entropy change with decreasing crystal size to interfacial effects. This statistical mechanical model reveals the in-depth ferroelectric polymers producing the ECE and offers significant potential for predicting the ECE in ferroelectric polymers and thus guides the design of high-performance ECE materials.