How do I sort folders by actual size, instead of amount of sub-folders or files

At least there is a GUI tool called baobab which you pretty sure have to install. I am sure there are more GUI tools out there. Just use your favorite search engine to find others.

On the command line, there is ncdu which does the job you want. Otherwise you could use plain command line tools like follows.

du -h --max-depth=1 <folder-to-check> | sort -h
du -h --max-depth=1 /etc/ | sort -h

I think all of them will output files and directories.

As mentioned by Thomas in his answer, you should use Disk Usage Analyzer app, aka Baobab. The default file manager, Nautilus, doesn't have a setting for displaying directory usage in bytes.

Command-line alternative to that would be ncdu , which you can get with sudo apt-get install ncdu

Great GUI tool called Baobab (aka Disk Usage Analyzer). I am especially in love with the interactive radial maps, which do a wonderful job at showing percent of usage per folder and sub-folder trees. Takes only seconds to drill down and see where those space hogs are.

To install

sudo apt-get install baobab 

To run

gksu baobab

If running on an encrypted drive, scan that particular one by going to the main page and then pressing the three lines in the upper right corner and choosing the sub-file (like home if it is encrypted).