Everyday objects and tools, such as power drills and game controllers, are predominantly designed with interfaces optimized for the grasping hand, enabling users to interact while maintaining a secure hold. Despite their ubiquity in daily tasks, designing these interfaces often relies on arbitrary processes influenced by basic ergonomic guidelines and driven primarily by industrial standardization. A critical challenge persists in developing personalized, hand-reachable interfaces that accommodate individual grasping conditions effectively. This requires properly understanding the hand physiological constraints and the hand-object interaction to create unique interfaces tailored to each user's specific needs. To address these challenges, I propose a novel empirical design framework that prioritizes characterizing the user's hand reachability (while grasping an object) as the first step in the design process. Recent advances in egocentric data collection and parametric and generative design technologies present new opportunities to reduce the workload of developing customized interfaces. By leveraging hand-tracking technologies, the proposed framework generates kinematic profiles that capture individual finger reachability during object grasping. To enable this, a system was developed that explored and offered a systematic method to create volumetric boundaries and trajectories from user data, which can then be incorporated into 3D modeling tools. These personalized profiles can illustrate optimal areas for user interface (UI) element placement based on reachability. It also incorporates physiological cost analysis, including electromyography (EMG) capture and displacement cost metrics, to evaluate physical effort within the user’s reachable space. As part of this work, a formative pilot was conducted to evaluate the system's functionality and inform improvements for future evaluations. This user-centric approach aims to shift the design paradigm and foment new design practices that leverage emerging technologies to adapt new interface designs to the user rather than requiring the user to conform to a generic design.