du -hs *; # check size of all directories in the current directory
du -hs Library/; # check size of a single directory
1.9G	Library/

tested with: 
Debian Linux 3.2.0-0.bpo.4-amd64 #1 SMP Debian 3.2.65-1+deb7u2~bpo60+1 x86_64 GNU/Linux
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