Transformational theory has long provided powerful models for understanding abstract pitch relations in music. While De Souza (2017), Frederick (2024), and Momii (2020) have begun integrating the physicality of performance into analytical models, the unique spatial and ergonomic constraints of the piano keyboard have yet to be systematically formalized within transformational theory. This paper addresses this critical gap by introducing Keyboard Distance (KD), an analytical tool that describes and calculates the gestural topography of keyboard music — the physical paths a performers hands travel. The KD quantifies physical distance on the keyboard. It defines the space between adjacent white keys as 1 unit, all other distances are measured proportionally according to the standard keyboard layout. By bridging the gap between abstract transformational theory and embodied performance practice, KD does not merely add a new analytical parameter; it argues for a more holistic understanding of musical structure where the physical interface of the instrument is recognized as a fundamental generative force. This model integrates the discourse on instrument-specific transformation theory, arguing that the physical design of the keyboard is not a separate concern but is fundamental to the music itself; that is, by prioritizing the performers embodied experience, especially the topography and the nature of black/white keys, KD offers a new perspective for understanding how composers exploit the instruments unique transformation space, affirming the pianos distinct identity within musical transformation studies.