When dealing with large files in MC, I have difficulties counting the digits to get the order of magnitude of the file size (hundreds of MB, or tens of GB, etc.). Sometimes, I use the trick to press insert key, which highlights the file and shows the file size in a nicely formatted way (i.e. 123,456,789), which makes it a thousand times more readable.
You can modify the configuration:
You can adjust the displayed digits with the column size option, see the “Listing mode” section in the manual. The file to edit is ~/.config/mc/panels.ini.
To list the file sizes as K, M or G use a narrow size column using the user_format key:
[New Left Panel]
user_format=half type name mark size:4 space mtime