<p>Multi-component polymer systems exhibit exceptional versatility and structural diversity, making them indispensable in the polymer industry as well as in advanced and high performance applications. However, constructing accurate phase diagrams for these systems remains challenging due to inhomogeneous structures arising from the introduction of block copolymer components. Here, we present a unified and model-agnostic framework for computing phase equilibria in multi-component polymeric systems based on the concept of “effective chemical potential”. This approach directly connects key thermodynamic variables in the canonical ensemble to other ensembles, unifying phase coexistence determination without requiring the reformulation of self-consistent field theory (SCFT) calculations across different ensembles. By decoupling phase equilibrium determination from specific ensemble formulations, our approach enables the reuse of existing SCFT solvers. Moreover, it provides a useful framework to develop highly efficient phase equilibrium solvers for multi-component polymer systems.</p>