How exactly is the act graded?

How exactly is the act graded?
I know its the average of the subscores for each section. But how many points is each question worth in each section? What’s the most points someone could miss and still get a 31? How does your Writing score play into it? Is it just a different score all together and will not affect your overall score?

The best source of information to answer your questions is ACT, Inc. itself:…

So, in the English section, you could perhaps miss two questions (out of 40) in Mechanics, and 1 question (out of 35) in Rhetorical Skills, and perhaps still get a 31 scale score for the English section.

The Writing test is an optional part of the ACT battery. Not every college or university will ask for it, and not taking it will not affect your Composite score or your subject area scores, from other sections of the ACT test.…
“… Your essay will be scored holistically—that is, on the basis of the overall impression created by all the elements of the writing. Two trained readers will score your essay, each giving it a rating from 1 (low) to 6 (high).

The sum of those ratings is your Writing subscore, which can range from 2 to 12.

If the readers’ ratings disagree by more than one point, a third reader will evaluate your essay and resolve the discrepancy.”

I would suggest you also download and study the free “Using Your ACT Result” file, in .pdf format: