This is the 4324th most frequent Korean word.
크기의
"크기의" means "of size" or "size of."
In this sentence, '크기의' is used as an adjective describing '문서들' (papers) to indicate their different sizes.
이 상자는 여러 크기의 문서를 보관할 수 있습니다.
This box can store papers of various sizes.
Here, '크기의' is qualifying '가구' (furniture) to signify that the furniture varies in size.
각 방은 다른 크기의 가구로 채워져 있습니다.
Each room is furnished with furniture of different sizes.
The word '크기의' is modifying '도시' (city) to specify that the city has a particular size or dimension.