Hi, I am a student taking the french baccalaureat. Thefore, my grades are out of 20 and I don’t know how to calculate my gpa. I’ve converted all my grades into letters, how can I now find out what my gpa is?
Don’t convert your grades or your grade point average unless you are explicitly instructed to. Otherwise, report your grades exactly as given. Most application forms, in particular the Common App, will give you space to explain what scale your GPA is on. For example, my high school GPA from Germany was 1.5 on a scale from 1 (best) to 6.
If you are explicitly asked to produce a GPA on a 4.0 scale, you would first convert every French grade to an American letter grade, and then take the average of the letter grades. Don’t forget to include a chart that shows the cross-walk between French grades and American grades you used, because different organizations use different cross-walks.
Actually, if you are explicitly asked, the college will tell you how to convert. If they don’t, ask them. But as mentioned above, if they don’t ask (and most do not) report the grades on the 20 point scale.
Trust @b@r!um on this 
Most colleges and unis prefer to do their own conversions.
However students often need to make internal conversions to see where they’re competitive.
Typically 13=A, 10= B, 7-8= C, 5= D.
Someone with 15+ moyenne at a school with a typical grade deflation compared to the bac you’re good everywhere (where moyenne is -1 compared to typical bac - that’d be a school with 85% bac, -1 added per 5 so deflation -2 for 90, -3 for 95% school etc. - so if your school is one of these 95% bac schools you could be fine with 13-13.5 if that typically results in a mention TB for your school… And if our school only has 78% for the bac then you’d need a 15-16.)