Here is a command with the flags to give you the bottom-line on your disk usage:
du -chs <somedir>
The key here is "summarize", if you only want the disk usage for each argument.
Where:
-c, --total
produce a grand total
-h, --human-readable
print sizes in human readable format (e.g., 1K 234M 2G)
-s, --summarize
display only a total for each argument