Understand the Size of directories

[root@auqldtv01act1ai /]# du -chx --max-depth=1

13M     ./sbin

47M     ./boot

12K     ./dumps

9.6G    ./tmp

8.5K    ./act_pri_pool000

269M    ./lib

12M     ./opt

4.0K    ./media

22M     ./lib64

20K     ./lost+found

0       ./dev

563M    ./act