Finder > Show View Options > Calculate all sizes
This option causes Finder to calculate the sizes of all files and folders and display their sizes in the Finder list view columns, rather than a useless --.
"Calculate all sizes" is OFF by default. I seem to need to enable it on a per-folder basis for every directory in Finder.
How can I enable "Calculate all sizes" as ON by default for all Finder folders?
Are there any performance considerations for this option on a modern Mac and APFS file system? Sizes are listed instantaneously and I have noticed no downside to enabling the option.
Best Answer
There's a catch to the accepted practise…
check 'calculate all sizes', then click "Use as Defaults".
Whilst it's true that setting "Use as Defaults" will change the pref for all future & containing folders, it is only true if no folder inside that hierarchy was ever previously set.
In effect it is "Set as default for all folders without an existing default."
To reset defaults, hold Opt ⌥ & the button will change from "Use as Defaults" to "Restore to defaults". If at any time this button is grey, then the folder is already at Default.
As to the second part; as far as I'm aware the Mac caches the sizes once calculated. Calculating for a big old spinny rust with terabytes of data takes quite some time initially, but going back later seems instant. I'm not sure whether this survives through reboot.