Given the prominence of international instructors in higher education, understanding their grading practices is essential for informing college grading debates. This first large-scale assessment of undergraduate grading practices highlights how different demographic, classroom and departmental factors shape international instructors' grading behaviors. Using a unique dataset of over 2,000 randomly selected instructors from three public universities, we examine (a) whether undergraduate-level grading practices differ between domestic and international instructors, (b) what factors contribute to the differences, and (c) whether the differences vary across key subgroups. We find that international instructors grade lower than domestic instructors--about 35% of a standard deviation lower on average. Part of this gap is explained by the concentration of international instructors in particular departments. International instructor grading practices differ across regions of origin, prior U.S. higher education experience, gender, and race. Our results provide insights into U.S. college grading debates and supporting the international instructor workforce.