What's Using Space
Open it from the More menu ••• → What's Using Space, or the What's Using Space tile on the Home screen. (Some screens call the same window the Storage Inspector — the menus use the plainer name.)
Everything here is measured on your Mac, not estimated. That's meant literally: where a figure can't be established, Storage Studio says so rather than filling the gap with a guess. Measure again walks your disk afresh, and results appear as they arrive instead of making you wait for the whole pass to finish.
What changed
The top section, and usually the one you came for. It compares this measurement against the previous one, over the exact window between the two readings:
- Gone — room taken by files that weren't there last time. Deleting
these gives the space back.
- Pinned — space held by your Mac's own recent backup snapshots of
files you've already deleted. Deleting more won't return it.
- Reclaimed — space released since the last reading, with nothing for
you to do.
The first time you open it there's no earlier reading to compare against, and it says exactly that rather than showing zeroes.
Biggest on this disk
Your largest folders, biggest first — and you can drill into any of them to any depth to find what's actually responsible, rather than stopping at a top-level folder that only tells you which room the mess is in.
Folders appear as each one finishes being measured, so the list fills in rather than blocking. Any row can be revealed in Finder, and Collapse all resets the view. A folder macOS won't let any app read is called out as unreadable, never silently counted as empty.
Space held by backups
How much room your Mac's local snapshots are holding — and how old it is. The heading gives you the headline immediately: how much is held, and how old the oldest snapshot is.
Each snapshot is listed with its age and when it was created, a plain description of why it exists (a restore point made before a system update, or a routine automatic one), and what can be done about it: required by macOS, your Mac can clear this by itself, or not marked clearable.
One honest caveat: macOS reports a single combined figure for all local snapshots and no size for any individual one. Storage Studio shows the combined total and says so, rather than dividing it up into numbers it would be making up.
A button alongside opens the Local Snapshots manager if you want to review or release them now.
Known quick wins
Collapsed by default: the well-known caches and leftovers, with a count of how many are already empty — so a long list of nothing doesn't crowd out the real findings.
How much was covered
The footer never overstates its reach. If parts of your disk are off limits to any app, or measuring stopped early to stay out of your way, it says so and tells you what the figures do and don't include.
Emptying the Trash isn't offered here either. It's the one action that can't be undone, so it stays your decision.
Relocated
Relocated in the header opens the list of everything currently moved to your fast drive, each with a one-click Move back. This is where a move is undone — and it's worth being clear about what a move is: your folder keeps working because a link is left in its place, but the files themselves now live on the fast drive, so they're reachable while it's connected and not while it isn't.