How to show file sizes In Midnight Commander in the most compact form? ("smart file sizes" in Total Commander)

Option 1: Using the interface

Change it in one of the panels by

1. Pressing F9
2. Choose Left (or Right)
3. Select Listing format...
4. Check User defined: and set the size string to size:4 and sekect OK. It should look like this:

     ┌────────────── Listing format ──────────────┐
     │ ( ) Full file list                         │
     │ ( ) Brief file list: 2        [^] columns  │
     │ ( ) Long file list                         │
     │ (*) User defined:                          │
     │ half type name | size:4 | perm         [^] │
     ├────────────────────────────────────────────┤
     │ [ ] User mini status                       │
     │ half type name | size | perm           [^] │
     ├────────────────────────────────────────────┤
     │            [< OK >] [ Cancel ]             │
     └────────────────────────────────────────────┘
   

5. To make it permanent, F9 > Options > Save setup.

Option 2: Editing the configuration file

Edit the file ~/.config/mc/panels.ini. There should be two user_format= entries, one under [New Left Panel] and other under [New Right Panel]. Change the entry of the desired panel to

user_format=half type name | size:4 | perm

The documentation

The relevant quote of the documentation, under Listing Format...:

To force one field to a fixed size (a size specifier), you just add : followed by the number of characters you want the field to have. If the number is followed by the symbol +, then the size specifies the minimal field size - if the program finds out that there is more space on the screen, it will then expand that field.

Therefore, bsize:4 is also possible. It is equal to size:4, except that for directories it just shows SUB-DIR or UP--DIR.