Do UC's and ivies use WES to convert international GPA's?

Hello! I could really use some help.
I’m a highschool student from Slovenia, who has just finished freshman year. I’m having some trouble calculating my GPA.
Long story short, we have grades from 1-5 (1 being a fail, 5 the best you can do). I’ve always thought that 4 is equivalent to a B and 5 to an A, but some websites state that 4 AND 5 are both equivalent to a US A, so that would obviously change my GPA drastically.
I’ve contacted the USA Education Slovenia institute here and they told me that most organisations such as WES (World Education Services) convert our grades 4,5 to an A, rather than 4 to a B.
My question is, how many universities actually follow these rules set by WES? I’ve seen Yale and UCLA on the partners list, does that mean that they convert GPA according to WES? Or can they still do it according to their own rules?
Thank you.

I believe Yale uses WES for grad school admissions, but not for undergrad, so my guess is that Ivy League schools do their own thing. File it under “it is what it is.” because there’s nothing you can do.

I believe the same holds true for UCLA. But I need to point out that UCLA (like all UCs) provides no financial aid to international students.

Each college and university should have information right on its website about transcript evaluation. Some will require it. Some won’t. Some will use WES. Some will specify a different evaluator. If you cannot find the information on the website, contact the international admissions office and ask them. It really, truly, is OK for you to ask them!