Du

du is acronymic for disk usage

When this command is called with no parameters, it will display the amount of disk space used by each file and directory under the currenct working directory (see pwd).

Most common flags:

-d -- used with a number to specify how many levels deep to search
-h -- use unit suffixes for sizes so as to make them human-readable

[light@splat ~/www/paint_fx]$ du
484     ./Graphics
522     .

[light@splat ~/www/paint_fx]$ du -d 0
522     .

[light@splat ~/www/paint_fx]$ du -h
484K    ./Graphics
522K    .