With the growing economic importance of open source, we need to improve our understanding of how open source software development processes work. The analysis of code contributions to open source projects is an important part of such research. In this paper we analyze the size of code contributions to more than 9,000 open source projects. We review the total distribution and distinguish three categories of code contributions using a size-based heuristic: single focused commits, aggregate team contributions, and repository refactorings. We find that both the overall distribution and the individual categories follow a power law. We also suggest that distinguishing these commit categories by size will benefit future analyses.