Q I'm not sure how Korean sizes work and how they would be converted to US sizing, but I'm looking for something around the sizes 4 - 6 (Small) or if this article runs small then maybe 1 size up.
(https://www.fila.co.kr/product/view.asp?ProductNo=42238)
A Hi, here is how to figure out the size for FILA KOREA items.
Click '사이즈 정보' (size info)

And you can see the details for each size.
상의 means top (jacket, shirts, etc.)

Here is the translation for you.

If you have more questions or concerns, please do not hesitate to contact us.
Thanks.
And maybe you can refer to this one, too :) https://weshipyourorder.com/article/a-guide-to-shoe-and-clothing-sizes-in-korea.html