What is 16 out of 24 as a grade

16 out of 24 would equal around 67%, and that as a grade would be a D.
However, grades MAY vary from school to school.
But on average:
A= 100 through 90, B= 89 through 80, C= 79 through 70, D= 69 through 60, and an F= 59 and below that.
Keep in my mind that if your grade has digits after the decimal, it will be rounded (in your case) and that may also change your grade, for example if your grade is 79.7%, then it will be rounded to 80%, and your grade will be a B.