I did the mathematics and I did all the snobby, dorky calculations. In my opinion, this is the most accurate possible scale that I could think of that equally coordinates letter grades with /10 number scores. For just judging movies and music, of course.
A+ —> 100 or 10/10
A —> 92 or 9/10
A- —> 85 or 8-9/10
B+ —> 77 or 8/10
B —> 69 or 7/10
B- —> 62 or 6/10
C+ —> 54 or 5/10
C —> 46 or 5/10
C- —> 38 or 4/10
D+ —> 31 or 3/10
D —> 23 or 2/10
D- —> 15 or 1-2/10
F —> 8 or 1/10
I will be updating the grades that I have given movies from 2019 and onward.