Although scale has been identified as one of four major interdisciplinary themes that cut across the science domains by the American Association for the Advancement of Science (1989), we are only beginning to understand how students learn and apply scale concepts. Early research on learning scale tended to focus on perceptions of linear distances, navigation and way finding, whereas more recent work has examined how students conceptualize scale in science contexts. This study sought to understand how understandings of scale develop from childhood to adulthood by asking 50 professionals to reflect on their experiences (in and out-of-school) learning about scale. Semi-structured interviews were utilized to obtain information about educational experiences, informal experiences, and applications of scale in different professions. Results showed that most of the participants used anchor points as conceptual benchmarks when applying scale in their job. Seventy-six percent of the participants attributed physical experiences such as moving through the environment by car, walking, bicycling, or flying in an airplane as contributing to the development of a sense of scale. Results of this study were used to develop a possible model of the trajectory of scale concepts that develop as individuals move from novice through increasing degrees of expertise. Across professions, participants emphasized the critical role that scale plays in their work. For many, scale was viewed as central to accomplishing the work-related tasks. (Contains 1 table and 1 figure.)