Write down your letter grade from all non-elective classes. Add any electives and AP courses considered as weighted courses, such as computer programming or a foreign language, to your list. Ask your school counselor if you have any questions about which classes to include.
Assign a number to each letter grade on a sliding scale. An A+ would receive a four, while an A- would receive a 3.7, a B gets a 3.2 and so on. If your school doesn't use pluses or minuses, then an A receives a four, a B a three and so on..
Add an additional point to any AP classes. For example, an A+ in AP English would translate into a five, while a B- would receive a four. AP classes receive more weight because they are considered comparable to a freshman level collegiate course.
Multiply each number by the number of credit hours that class was worth. For example, if you received a B- in a three-hour English class, you'd multiple three by three to get nine. If your school does not use the credit hour system, treat each class as one credit.
Add up all of your classes and then divide the number by the total number of credit hours to find your weighted GPA. For example, four A+s and three B-s in seven classes worth three credit hours each would translate into a GPA of 3.57.