The rapidly growing field of nanoscience and nanotechnology calls for the inclusion of general nano-education in our educational agenda. Student understanding of one of the key concepts in nanoscience, size and scale, serves as a prerequisite for students' learning of more advanced nanoscale science and technology. This paper presents the findings of a small-scale qualitative study with students studying nanoscale science aimed at exploring the ways they understand the idea of "size and scale". Results suggest wide variation in the way students understand this concept. The study identifies a preliminary typology of student conceptions of size and scale as it relates to macro and sub-macro phenomena along three key dimensions. In addition, the research identified a critical paradigmatic experience which appears to play a role in hindering the development of more complex and sophisticated understanding at each level of conception.