There's no way to get around the fact that your GPA is extremely important for gaining acceptance to PA school. When it comes to calculating your overall or science GPA, it is much more involved than taking a simple average of all of your grades. In this post, I'm going to explain how your GPA is calculated for CASPA since that is what the schools will be looking at. Nothing stinks more than to do the wrong calculations, think you have a 3.2, and then CASPA calculates at a 2.9. That completely alters the plan of where you'll be able to apply! The reason CASPA does these extensive calculations is to standardize GPAs across all colleges and universities is so PA programs can compare students as fairly as possible.
CASPA takes into account how many hours each course was, as well as the grade. This is called "Quality Points." These points are calculated by multiplying the amount of credit hours by the grade you received. For example, if you took a 4 hr course, and made a B, this would count as 12 quality points (4 x 3.0 = 12). To calculate your overall GPA, you divide the total amount of quality points by the total amount of credits. If you have 50 quality points, and 20 credits, that would result in a 2.5 GPA. All calculations are done based on the semester system. If you have quarter hours these will convert at 1 quarter hour = 0.667 semester hours.
There are multiple categories that are calculated separately. Each year is separated (freshman, sophomore, junior, senior, post-baccalaureate, and graduate) and then there is science and non-science. The subjects in the science GPA include Biology/Zoology, Inorganic Chemistry, Biochemistry, Organic Chemistry, Physics, and Other Sciences. You will choose what category courses fit into when you enter your courses, but these may be changed during the verification process if it appears that a course was entered incorrectly.
CASPA includes all grades in it's calculations, including courses that have been repeated. When some undergraduate programs calculate GPAs on transcripts, they will sometimes only include the grade from after the course has been repeated, which will result in an inaccurate number. Withdrawals are not included in the CASPA calculations unless they are "WF," which will count as an F. Pass/fail and AP credits are counted similarly to the W, and just as credits without associated grades. On the website with information pertaining to GPAs, CASPA has some great charts pertaining to how they count different letter grades and how grades are converted in both the US and Canada.
PA programs use these calculated GPAs differently. Some will take exactly what is calculated by CASPA with no modifications. Other programs will recalculate the GPA based on the highest grade after retaking courses or based solely on the last 45 or 60 hours of coursework. They may still look at the overall CASPA numbers, but they will place different weight on these calculations if they do their own.