The main purpose of this study was to develop a Rasch Measurement Physical Fitness Scale (RMPFS) based on physical fitness indicators routinely used in Hong Kong primary schools. A total of 9,439 records of students' performances on physical fitness indicators, retrieved from the database of a Hong Kong primary school, were used to develop the Rasch scale. Following a series of iterative Rasch analyses that adopted the "data should fit the model" approach, four physical fitness indicators (i.e., 6-min run, 9-min run, 1-min sit-ups, and dominant handgrip) were successfully calibrated to form the RMPFS. The RMPFS and its scale indicators showed fit to the Rasch model sufficient for the intended purposes of measuring the overall fitness of children. The overall physical fitness measure reflects children's fitness on three key core components of physical fitness (i.e., cardio-respiratory fitness, muscular endurance, and muscular strength). Advantages of the RMPFS are discussed, and recommendations for future research follow. The findings of this study provide a better knowledge basis for interpreting children's physical fitness assessment results. (Contains 1 footnote, 5 tables, and 4 figures.)