How to See Folder Sizes on a Mac (Why Finder Shows “--”)

Open any folder in Finder’s List view and look at the Size column: files get real numbers, folders get --. It looks broken; it’s actually a deliberate trade-off, and the details are further down. First, the ways around it — each with its catch.

Get Info, and its underrated sibling#

Select a folder and press ⌘I. The Get Info window computes the real size — watch it count up on big folders.

For several folders, don’t select them all and press ⌘I — that opens a separate window for each. Press ⌘⌥I instead: the single Inspector window updates live as your selection changes, and shows the combined size of everything selected. It’s one of Finder’s best-kept secrets.

Making the Size column real#

Warning

This method recalculates continuously for every folder in every window where it's enabled. On large directories or network volumes that's real CPU and disk I/O, spent mostly on sizes you aren't looking at — which is exactly why Apple ships it off by default.

To get actual sizes for every folder in a window:

Switch the folder to List view (⌘2).
Press ⌘J to open View Options.
Check Calculate all sizes — and optionally Use as Defaults to apply it everywhere List view is used.

Folders now show true sizes, and sorting by the Size column finally works — the -- entries no longer clump uselessly at the bottom.

`du`, for the Terminal-inclined#

The classic. cd to the directory you care about and run:

du -sh *

-s summarizes each item instead of listing every subdirectory; -h prints human-readable units. Pipe through sort to find the space hogs:

du -sh * | sort -h

Worth knowing before you compare numbers: du measures allocated disk blocks and counts hidden files, while Get Info reports logical size — small differences between them are normal, and both are “right” by their own definition. Also, for protected locations (parts of ~/Library, other users’ folders) Terminal needs Full Disk Access — System Settings → Privacy & Security — or you’ll get permission errors and undercounted totals.

Why Finder leaves sizes blank#

A file’s size is stored metadata — free to display. A folder’s size is not stored anywhere: the only way to know it is to walk every file inside, including every nested subfolder, and add them up. For something like ~/Library that can mean touching hundreds of thousands of files. Finder skips it by default so directory listings stay instant.

Reasonable engineering. The problem is the menu of options it leaves you: never (the default), always (Calculate all sizes, and pay for it constantly), or somewhere else (Get Info windows, a Terminal).

The option Apple didn’t build#

The one missing from that menu is the one you actually want: this folder, right now.