For human-readable output use the following command:
```bash
du -sh /* | sort -h
```
Use this command to find the directories taking up the most space:
```bash
du -k | sort -nr | more
```
The **du** command along with the **-k** switch lists all directories and their respective size in kilobytes.
The **sort** command sorts the output so that the largest directory is shown first in the list. The **-nr** switch reverses the list and uses only numbers when sorting.
Here's an example of the output:
```bash
12939451 .
1814892 ./abcdef
1219582 ./abcde
839586 ./abcd
718330 ./abc
695610 ./ab
690380 ./a
```