Are SAT Subject tests required for admissions? If so, how many?
Generally… No.
USC only requires SAT Subject tests from first-year applicants who do not attend a regionally accredited high school (such as home school, some non-accredited parochial or community based programs, even some newer schools). Such students must submit three SAT Subject exams, including one in mathematics, in addition to the SAT or ACT.
For all other applicants, these exams are optional.
Here is a link to the USC webpage detailing all requirements for Admissions:
http://www.usc.edu/admission/undergraduate/faq/admission_standards.html
Good Luck…
If you are engineering, I’d suggest them strongly though, one science, one math. And if you took any others and scores are good, submit them. But not required.