Unreinforced masonry (URM) infill walls, although classified as non-structural elements, significantly affect the seismic performance of reinforced concrete (RC) frame buildings, especially due to their vulnerability to out-of-plane (OOP) collapse. Building upon a previously developed analytical model, this study presents an extensive parametric analysis aimed at investigating the influence of key parameters—namely aspect ratio (L/H), slenderness (H/t), masonry strength, and perforation direction—on the OOP capacity of URM infills. The analysis covers a broad range of configurations to assess the sensitivity of OOP behaviour to geometric and mechanical variations. The results are synthesised into simplified design charts intended to support engineers in the preliminary assessment and verification of URM infills under OOP seismic actions. These charts offer a practical tool for incorporating OOP performance considerations in seismic design and vulnerability assessments.