My GPA is a 3.556. My class size is 351. So that boils down to about a 14%.
Not quite sure how you derive that third fact from the first two.
When my daughter applied to colleges, she was also in the middle of the second decile. It probably did contribute to her being wait-listed at one university that was a little bit reachy for her, where they seem very
interested in class rank.
But remember, class rank is far from the only admissions criterion. Colleges and universities will be looking at your transcript--not only to see your grades, but also to see what kind of classes you took--and your standardized test scores. In most cases, they will use your class rank to get a sense of what a 3.56 means in your high school. (And it means more in your school, apparently, than it would in my kids' school. In my kids' school, it would probably put you in the fourth decile.)
My question is, will colleges consider this to be top 25% or will they consider it as a 14%?
Some of both, I'd guess.
Missing the top 10% can be a big miss, unfortunately. Colleges report the HS class rank of incoming freshmen on the Common Data Set. And they all report it the same way (which is what makes the Common Data Set "common"--all institutions use the same format). They report HS GPA in bands: top 10%, top 25%, top half. If you're top 11% or 12% or 14%, and you eventually enroll, they'll have to report you as top quarter, but they won't get to round you up to top tenth. This is why the difference between top 10% and top 12% probably counts a lot more than the difference between top 12% and top 14% (or top 8% and top 10%, for that matter).
On the other hand, when they're trying to get a sense of what your GPA means, they will want more information than just "top quarter." For this purpose (again, I'd guess) they will want to know that you were in the middle of the second decile, and not the middle of the third decile.