Editor’s note: Last updated on September 15, 2019.

Parents and prospective students are often interested in the average size of course sections. Assessing class size is extremely difficult because, first, a “class” has to be defined. Why is that difficult?

Some main sections (often in intro science, economics, business, etc.) may be very large, well in excess of 100 students, but the breakout labs and discussion sections are much smaller. Should  only the main section be counted, or should the labs and discussion sections also be included?

The best source for class size information and interesting data in general is the Common Data Set. Some universities publish their submissions, while others do not. The data in the CDS are used by U.S. News for many purposes, including the calculation of the percentage of classes with fewer than 20 students and the percentage of classes with more than 50 students. Using that information, we can also calculate the percentage of classes with enrollments between 20 and 50 students.

U.S. News does not include tutorials, thesis research, lab or discussion sections, and neither do we in our estimates of class sizes for honors programs. According to our counts, the average public university honors-only class section has 17.54 students. When we include honors credit classes that also have non-honors students, the overall average class size is 24.9 students. Both of these numbers are better than in 2016. This is an important consideration, given that the tables below show that public universities as a whole have significantly larger class sizes, and several have increased over 2016.

The next level of difficulty when using U.S. News data is to plug in an average number for the three class size groupings. For the group of fewer than 20 students, we are using an average of 17.5 students per section; for the group of classes with 20-50 students, we are using an average of 35 students; and for the group of classes with more than 50 students, we are using an average of 110 students.

The table below shows the percentage of classes in each size category along with the increase or decrease in the overall class size average since 2016. Universities are in rank order according to lowest estimated overall class size in 2020.