What is the singular possessive of campus?

There are two accepted forms for a possessive singular that ends in s:

Add an apostrophe s ('s) after the existing s at the end of the Word.

Example: The campus's size is about eight acres.

Add an apostrophe (') after the existing s at the end of the Word.

Example: The campus' size is about eight acres.

Note: The -s's is the most commonly used form, but if you are a student, use the form that is preferred by your teacher.