Here are some examples on how to find a directory size in linux:
This will show you the directory size of /var/www/vhosts/marianzburlea.com
du -h /var/www/vhosts/marianzburlea.com
This command gives you a better output than the default one. The option '-h' stands for human readable format. So the sizes of the files / directories are this time suffixed with a 'k' if its kilobytes and 'M' if its Megabytes and 'G' if its Gigabytes.
du -c /var/www/vhosts/marianzburlea.com
This gives you a grand total as the last line of the output. So if your directory has a total size of 225MB the last 2 lines of the output would be.