Grades: science/non-science, weighted GPA
Your science GPA will be a weighted average of grades in Biology, Chemistry, Physics and Mathematics courses that you take, at Williams and elsewhere. While Williams gives all courses equal weight, courses with laboratories are given more credit in the medical school admission process. At Williams, a standard course without lab is credited with 3.25 semester hours. Laboratory Biology and Physics courses are given 4.75 semester hours of credit, while lab Chemistry courses are given 5.25 hours of credit, due to their longer labs.
In general, this means that a GPA for the purpose of medical school admission will be slightly different from the GPA on your Williams transcript, and it will tip in the direction of your lab science grades.