Batch production is common in repetitive construction projects, and it is not unusual for different batch sizes to be used by contractors in one project. While several scheduling methods, such as the Linear Scheduling Method (LSM) and the Repetitive Scheduling Method (RSM) have been proposed and used, no mathematical method for repetitive construction projects has been developed, and it is difficult to consider different batch sizes with the existing methods. An original mathematical algorithm for scheduling repetitive projects with different batch sizes is proposed in this study. This algorithm is illustrated with assumptions of resource continuity and single path in a project and introduces new terms, control batch and critical batch. The algorithm logics and mathematical equations are validated by comparison with the outcomes from a graphical scheduling approach through a simple and practical hypothetic project. As a result, it is expected that the proposed algorithm can be easily adapted and extended to computer software for scheduling, and can be a starting point for research on batch size management in repetitive construction projects.