Find out the value of your school's weighted grade point average scale. Different school's can have different numerical values for A,B,C, D, and F so find out what g.p.a your school values each grade and write them down. For example, usually an A is a 4.0, but can be higher at other school's. School's assign the numerical value for letter grades, but the weighted GPA is essentially determined by combining your school's values with the total credits per course.
Request your college transcript from the registrar's office. Your transcript lists each course you have taken so far, how many credits each course is worth and what letter grade you received in each.
Look at one class at a time and multiply the grade you received and the number of credits the class is worth. If you received a B in a class, and your school considers at B a 3.25, and the class is worth 3 credits, you will multiply 3 x 3.25, which equals 9.75.
Add the totals of all of your classes together and divide by the number of credits you have taken so far in the year. For example, if you have taken two classes at three credits each, and the totals for each class are 9.99 and 10.00, your calculation will look like this; 19.99/6=3.33. According to this example, you GPA would be 3.33.