University size can be measured in several ways, including total enrollment, number of campuses, affiliated colleges and geographic reach.
Enrollment-based comparisons often feature open universities because distance-learning models allow institutions to serve students across large geographical areas. Affiliated-college networks and multi-campus systems can also accommodate substantial student populations.

However, rankings require consistent data. Enrollment figures may refer to different academic years, and a university should not automatically be compared with an entire statewide higher education system without explaining the distinction.
The Campus Review's guide explores large institutions, their educational models and the importance of understanding enrollment data.
Read more:
https://thecampusreview.com/study-abroad/largest-university-in-the-world/