Is there a chart/guide to know what master rank you'll get after a match?

I ask this because it seems a bit weird/unclear to me. I just went 11/1/25 with Jinx (Almost 11/0/25, but my traps missed trapping a garen and I got hit by his empowered Q attack :| RIP). Anyways, we finished the match after that and I only got an A rank. So...how was that not an S?

Was there more to it than what I did? Did I not have enough minion farm? Is there a guide on how ranks are established or not?

I mean, I'm sure this question has been asked many times before, but when it seems like I should be getting a certain rank, I don't. Like when I think I should get an S I instead get a B or A, or when I think I should have gotten a lower rank like a C I get an A or B even though I don't have a lot of kills.

So...has anyone or league released actual details on what determines it? Thanks in advance.