How do I find the size of a directory on a Unix-like command-line?

du -s directory, as in "disk usage, sum"

Use du -sk to show the size in kilobytes (default is to show number of 512-byte blocks), or du -sh for a more human-friendly output. For more options, type man du.

This is the same as -s, but replace 0 with 1 and you can get just the content in the folder:

du -h -d 0 /path/to/file

If you want the whole volume, you should use df instead of du (path is optional):

df -H /

Off-topic: One (very) spooky thing: I happend to be just a street away from Arne Stenström.

/Robert