While recent national and international assessments have shown mathematical progress being made by US students, little to no gains are evident in the areas of geometry and measurement. These reports also suggest that practicing teachers have traditionally had few opportunities to engage in content learning around topics in geometry and measurement. This article describes a set of assessment tasks designed to measure teachers' mathematical knowledge for teaching geometry and measurement in a nuanced way. The tasks, focused on relationships between measurable quantities of figures, adhere to three key design principles: Tasks are grounded in the context of teaching, measure common and specialized content knowledge, and capture nuanced performance beyond correct and incorrect answers. Six tasks are presented that reflect these design principles, with teacher data illustrating the ways in which the tasks differentiate performance and reveal important aspects of teacher knowledge.