Converting my A-level and IGCSE grades to a GPA scale?

I’m an international student from the UK who’s done IGCSEs, AS and am currently in year 13 (12th grade) finishing up with A2. Here are my grades:-

Old IGCSE:-
Maths, Physics, Biology, Chemistry, English literature: A*
English language, Economics, German: A
History: B

AS:-

Maths, further maths, physics: A
Chemistry: B

A2 predicted grades:-

Maths, further maths, physics: A* (dropped chemistry)

No idea what my GPA would be and would love some help because online sources haven’t been very useful as I have no idea if my grades are anywhere near competitive for some of the top American schools?

You have no idea if your A* and A grades are competitive? Yes.They are more than competitive.

Yes, your grades are competitive, but they are only a small portion of the admissions picture at very selective universities. American universities will also be considering your extra-curricular engagement (e.g. sports, academic competitions, community service), your financial resources, letters of recommendation, alumni relations, etc.

Or as Harvard once said: 90% of their applicants are academically qualified to attend, but they only have room for 5%. So they get to be choosy.