The About This Mac storage bar is the first place most people look when their Mac runs low on space. It is also one of the most misunderstood screens in all of macOS — the colors shift, the numbers lag, and the "Recommendations" panel often points at things you cannot safely touch. This walkthrough decodes every segment, explains why the bar is frequently inaccurate, and shows you how to get numbers you can actually act on.
How to Open the Storage Bar
- Click the Apple menu () in the top-left corner.
- Select About This Mac.
- On macOS Ventura and later, click More Info, then scroll to the Storage section. On macOS Monterey and earlier, click the Storage tab directly.
- Wait 10–30 seconds for the bar to finish calculating — it crawls the filesystem in the background and the first render is often a rough estimate.
What Each Color Segment Means
Apple uses a fixed palette of colors across macOS versions, though the exact shades vary between light and dark mode. Hover over any segment to see its label and size.
| Color (approximate) | Label | What it includes |
|---|---|---|
| Blue / Indigo | Apps | .app bundles in /Applications and ~/Applications |
| Purple / Plum | Books | Apple Books downloads |
| Teal / Green | Documents | Files in ~/Documents, ~/Desktop, ~/Downloads, and iCloud Drive local copies |
| Orange / Amber | Photos | Photos library (~/Pictures/Photos Library.photoslibrary) |
| Yellow | Mail message bodies and attachments (~/.Library/Mail) | |
| Pink / Rose | Music / Podcasts | Downloaded media in the Music and Podcasts apps |
| Gray (light) | System Data | Caches, logs, temporary files, Time Machine local snapshots, virtual machine images, developer data |
| Gray (dark) | macOS | The operating system itself — do not touch this |
| White / Hatched | Other | Files that do not fit any category above; can include large archive or disk image files |
Why the Numbers Are Often Wrong
The storage bar is a convenience summary, not a real-time measurement. Several factors make it unreliable:
- Staleness. macOS caches the scan result. After you delete files, the bar may not reflect the change for minutes or until the next login.
- Purgeable space. macOS optimizes storage by keeping iCloud-evicted file stubs, APFS snapshots, and cached downloads on disk but marking them "purgeable." These blocks appear occupied but macOS will reclaim them automatically when space is needed. The bar sometimes shows purgeable blocks as used, sometimes not — the display is inconsistent across versions.
- System Data is a catch-all. This is the single most complained-about segment. It lumps together legitimate OS caches, Time Machine local snapshots, Xcode derived data, iOS backups, virtual machine disks, and genuinely orphaned junk — with no breakdown.
- APFS volume sharing. On Apple Silicon Macs the System and Data volumes share a single APFS container. Space accounting across volumes can produce numbers that seem to add up to more than the disk's total capacity.
You can get a faster, unambiguous reading from the Terminal:
df -h /This shows actual available space as the filesystem sees it right now, with no caching delay.
The "Recommendations" Panel
When you click Manage (or Storage Settings on Ventura+), Apple presents four recommendations:
- Store in iCloud — uploads Desktop, Documents, and Photos to iCloud, keeping local stubs. Useful if you pay for iCloud storage and have a reliable connection.
- Optimize Storage — removes already-watched iTunes/TV purchases from local disk and keeps only recently played music. Safe if you have a good internet connection.
- Empty Trash Automatically — deletes items in Trash that are older than 30 days. Safe and worth enabling.
- Reduce Clutter — opens a file browser for Downloads, large files, and app installers. Useful for a first pass but it misses most of the real waste.
None of these recommendations touch caches, logs, or developer data — the categories that usually account for the largest recoverable space.
What Is Actually Inside System Data?
You can explore the main contributors yourself in Finder by pressing Shift-Command-G and navigating to these paths:
~/Library/Caches— per-user application caches. Generally safe to clear, but apps will rebuild them on next launch./Library/Caches— system-wide caches. Safe to clear with caution.~/Library/Application Support— app data including saved state, plugins, and support files. Do not bulk-delete this folder; it contains settings and data you may want to keep.~/Library/Logsand/Library/Logs— log files. Safe to delete.~/Library/Developer/Xcode/DerivedData— Xcode build artifacts. Safe to delete; Xcode will rebuild on next build.~/Library/Developer/CoreSimulator/Devices— iOS Simulator images. Each device image can be 2–8 GB; delete unused ones from Xcode's Devices window.
Deleting Safely vs. Unsafely
Before you delete anything, understand the risk tiers:
- Safe without concern: Trash, log files, Xcode DerivedData, app caches in ~/Library/Caches, iOS Simulator runtimes you no longer use.
- Safe but apps will be slower until they rebuild: All caches under ~/Library/Caches and /Library/Caches.
- Review before deleting: Files in ~/Library/Application Support — target specific app subfolders you know you no longer need.
- Do not delete: The macOS system volume, /System, /usr, /private, /Library/Extensions, your Photos library unless you have a verified backup, or any Keychain files.
Cleaning is permanent. The Trash is your safety net — move things there first if you are unsure, and only empty it when you have confirmed nothing broke.
Getting an Accurate Breakdown with Crumb
The Apple storage bar will not tell you which specific app owns those 18 GB in System Data, or whether a folder buried in Application Support is safe to remove. Crumb addresses this directly with its whole-Mac audit: it scans every category — caches, logs, app support folders, Time Machine snapshots, developer data — and presents each as a drillable list with actual byte counts. You can see the largest items, understand what owns them, and ask the built-in AI "is this safe to delete?" before touching anything.
If you want to go further, Crumb's Uninstall tab removes apps along with their leftover preference files and support folders that the About This Mac panel would keep counting under System Data indefinitely after a manual drag-to-Trash removal.
You can download Crumb and run one free cleanup to see what is actually taking up space.
Forcing the Storage Bar to Refresh
If the bar looks obviously stale after cleaning, try these steps in order:
- Close the About This Mac window and reopen it — the scan restarts.
- Log out and back in. The storage calculation daemon resets on login.
- If a large Time Machine local snapshot is inflating System Data, you can list and delete snapshots from Terminal:
# List local snapshots
tmutil listlocalsnapshots /
# Delete a specific snapshot (replace the date string)
tmutil deletelocalsnapshots 2025-11-14-120032After deleting snapshots, allow a minute for APFS to reclaim the blocks before reopening the bar.
Summary
The About This Mac storage bar is a reasonable first look, but it is too coarse and too slow to be your primary tool for reclaiming disk space. System Data in particular is a black box that hides the most actionable cleanup targets. Use the Finder paths and Terminal commands above to explore what is really there, follow the safe-vs-unsafe guidance before deleting anything, and reach for a drillable audit tool when the bar leaves you guessing.