HOW TO calculate my GPA if my school does not follow grading system

Lots of international students stumble upon this section of the application process, and then have no idea what to do. Many countries in the world have schools that do not follow the US grading system and insted have a percentage and marks out of 100 system. Most of us get on google and start searching for "how to calculate GPA??". But here's the deal. You don't have to in most cases. Most universities in US know that a large majority of  schools around the world follow the aggregate percentage based system, and not the letter-grade system followed by the US schools. And so most of them allow you to enter your aggregate percentage for the 8 semesters in the GPA box, just put a percentage sign (%) after the number. BUT, the keyword here is "most". Not all of them are quite happy with percentages, and in that case, you will have to somehow work out your GPA, which I will explain shortly.
But before that, shoot your school an email and ask them if percentages instead of GPA are ok. Most schools would mention it on their app forms, but some do not. And by sending them an email, you can make sure and not regret having wasted time/money on sending an incomplete application.

Anyways, so here is how GPA or the Grade Point Average system works and is calculated using your percentage based marksheets. Before you can calculate GPA, you should know how many credits each course you take is worth.

Now it is imperative you understand what these credits mean. A 4 credit-hour course (aka 4-credits) generally means that you would attend 4 hours of classes for this course per week. The cost of taking this course is also determined by the number of credits its worth. And, before you can you graduate from a US school, you need a certain number of credits in total. So you see how all of this adds up. A Master''s degree might be worth 32 credits. That simply means you have to take course whose total credits would add up to 32, and then and only then would you be awarded the Master's degree.

Anyways, a 4 credit course would cost you 4 * cost per credit for your school. This cost per credit hour varies vastly from one school to another. And remember, the cost for graduate and undergraduate credits is also different. Graduate credits are more expensive.

Moving further, once you know the credits your courses are worth, this is how you calculate your GPA:
Let's say in the 1st semester, you took two courses, P (a 3 credit course) and Q (a 4 credit course).
Now suppose your total score (which is a combination of your homeworks, programs, project work etc) at the end of the semester for P is 89% and Q is 93%. Generally the following grades are awarded (the cut-offs vary from one school to another or from professor to professor):-

Overall Score     Letter Grade       GPA
> 90                            A                    4.0
85-90                          A-                  3.77
80-85                          B+                 3.44
75-80                          B                   3.11
70-75                          B-                  2.78
65-70                          C                   2.45
you don't want to get any lower than this anyways :)

So, you scored 89% in P (grade A-) and 93% in Q (grade A). Here is what your GPA for the 1st semester (also known as CGPA: Cumulative GPA) will be:-

CGPA after 1 semester ==

3.77 * credits_for_P + 4 * credits_for_Q
-----------------------------------------
total credits taken (=7 for sem 1)

And that's the formula you should use for calculating your GPA for every semester of your BE, and then take an average. Simple, right? But again, for this to work you need to know the letter grades and what range of scores they correspond to.