Got the 'Storage Almost Full' Warning on Mac? Here's What to Do

The “Your disk is almost full” notification appears when free space drops below about 10% of your total drive. It’s not just a friendly suggestion — once you’re below that line, macOS starts behaving badly. Updates fail. Apps refuse to save. Browsers freeze. Photos won’t import.

The fix usually takes 30 minutes if you know where to look. Here’s the playbook, in order.

Don’t skip this: check the actual numbers

Before deleting anything, get a baseline. Apple menu → System Settings → General → Storage. Wait a full 30 seconds for the colored bar to populate accurately — it takes a moment to scan everything.

Note your current free space. You’ll want to compare after each step to see what worked. For most Macs, your goal is at least 20% free, and ideally 30%.

The categories you’ll see, ranked by typical bloat:

1. System Data (the big mystery — usually 50-150GB)
2. Applications (10-50GB depending on what you’ve installed)
3. Documents (highly variable)
4. iCloud Drive (if you’ve enabled it)
5. Mail, Photos, Music (varies)

System Data is almost always the biggest offender, and we’ll spend most of our time on it.

Step 1: The trivial 10-15 minute pass

These cost almost nothing and almost always free 5-15GB:

1. Empty the Trash. Right-click Trash icon → Empty.
2. Clear ~/Downloads of anything you haven’t opened in 3+ months.
3. Restart your Mac. macOS clears working files and snapshot remnants.

If you’ve done these recently, skip to Step 2. If not, do them first — they’re the easiest reclaimable space anywhere.

Reclaim 20+ gigs in one passSweep finds the caches, snapshots, and old downloads adding up to most of your “System Data.” Free download →

Step 2: Time Machine snapshots (often 5-30GB)

Even with no backup drive, macOS keeps APFS local snapshots on your boot drive. They’re invisible, count toward used space, and grow slowly over time.

Open Terminal and run:

tmutil listlocalsnapshots /

If you see entries (you almost certainly will), force aggressive thinning:

sudo tmutil thinlocalsnapshots / 9999999999 4

Expect to free 5-30GB in seconds. macOS will recreate snapshots later, but right now you’ve got space back.

Step 3: iOS backups (often 30-100GB)

If you’ve ever plugged an iPhone or iPad into this Mac, there’s almost certainly a backup taking serious space.

Open Finder, hit Cmd+Shift+G, paste ~/Library/Application Support/MobileSync/Backup/. Each subfolder is a device backup. Compare modification dates to your current device — keep the newest, delete the rest.

Or use Finder’s UI: plug in your current iOS device, click it in the sidebar, click Manage Backups. Delete old ones from the dialog.

A single backup can be 50GB+. This is often the single highest-value step in the whole guide.

Step 4: Mail attachments (5-20GB)

Apple Mail caches every attachment you’ve ever previewed. The cache lives at ~/Library/Mail/V10/MailData/ (the V10 might be V8 or V9 on older macOS — same idea).

Cleanest fix:

1. Open Mail
2. Mailbox menu → Rebuild on each large mailbox
3. Wait — this is slow, often 30+ minutes for big accounts

The rebuild re-downloads from the server and drops orphaned attachments. Cleaner than just deleting MailData files because it preserves your local mailboxes properly.

If you’d rather just stop the bleeding without a rebuild, set Mail → Settings → Accounts → your account → Account Information → “Download Attachments” to “Recent” or “None.”

Step 5: Big files lurking elsewhere

Spotlight is the fastest way to find oversized stragglers. Open Finder, Cmd+F, then:

• Where: This Mac
• Click “Kind” → change to “File Size”
• Set “is greater than 1 GB”

Sort the results by size. Look for:

• Old video projects (Movies folder, Documents folder)
• Virtual machine disk images (.vmdk, .qcow2, .vdi)
• Forgotten ZIP archives
• Database files from rarely-used apps
• Old GarageBand and Logic projects

For each, decide: delete, keep, or move to external. Most large files don’t need to live on your boot drive.

Step 6: Apps you don’t use

Open /Applications. Sort by Size. Look at the apps over 500MB you haven’t opened in months.

Drag to Trash, but understand: this leaves their support files behind. Folders to manually clean per app:

• ~/Library/Application Support/<app name> (often 1-5GB per heavy app)
• ~/Library/Caches/<app bundle id> (can be huge for Spotify, Slack, Adobe)
• ~/Library/Containers/<app bundle id> (sandboxed app data)
• ~/Library/Preferences/<app>.plist (small but adds up)
• ~/Library/Logs/<app> (occasionally large)

Doing this for one app: 5 minutes. Doing it for ten apps: an afternoon. Sweep’s app uninstaller does the whole hunt in one approval per app — no manual digging through Library folders. Either way, the goal is the same: don’t leave 5GB of leftovers per uninstalled app.

Step 7: Photos library (if applicable)

If you use Photos with iCloud Photos, check Photos → Settings → iCloud. If “Download Originals to this Mac” is on, your entire library is local — easily 100GB+ for a heavy iPhone user.

Switch to “Optimize Mac Storage.” Your Mac keeps thumbnails locally and pulls full resolution only when you open a photo. macOS thins the local copies over the next few hours.

The Photos library file itself (~/Pictures/Photos Library.photoslibrary) sometimes has bloated cache directories. If you want to be really aggressive: quit Photos, then right-click the library → Show Package Contents → look for resources/derivatives and caches. These can be cleaned without losing any photos, though Photos rebuilds them on next launch.

Let Sweep do this in one clickManual cleanup takes an hour. Sweep does it in 90 seconds, with a preview before anything’s removed. Get Sweep — free for Mac →

Step 8: Big caches you can clear directly

If you’re still not where you want to be, hit the heavy-hitter caches by hand. Quit each app first.

• Spotify: ~/Library/Caches/com.spotify.client/ (often 4-8GB)
• Slack: ~/Library/Application Support/Slack/Cache/
• Microsoft Teams: ~/Library/Application Support/Microsoft/Teams/
• Discord: ~/Library/Application Support/discord/Cache/
• Adobe (Photoshop/Premiere): ~/Library/Caches/Adobe/
• Chrome: ~/Library/Caches/Google/Chrome/

For browsers, also use the browser’s built-in clear-data tool to handle profile-folder caches.

Step 9: Xcode (if installed)

If Xcode is on your Mac, it’s almost certainly hoarding 20-60GB. Folders to nuke:

• ~/Library/Developer/Xcode/DerivedData/
• ~/Library/Developer/Xcode/iOS DeviceSupport/
• ~/Library/Developer/Xcode/Archives/ (only if you don’t need them for App Store submissions)
• ~/Library/Developer/CoreSimulator/Caches/

If you don’t actively use Xcode, just uninstall it. The full Xcode + caches + simulator runtimes is routinely 80GB.

Verify and set up auto-cleanup

After all steps, check Storage again. You should be at least 20% free, ideally 30%+.

Now prevent this from happening again:

• Finder → Preferences → Advanced → enable “Remove items from the Trash after 30 days”
• System Settings → General → Storage → enable “Optimize Storage” recommendation
• Set a quarterly Calendar reminder: “Quarterly Mac cleanup”

Honest assessment: macOS doesn’t clean these things automatically. Once you’ve cleaned, the cycle starts over. Caches grow, snapshots accumulate, Mail attachments pile up, Downloads bloats. In 6-12 months you’ll be doing this again unless you have a tool that maintains it for you.

That said, the steps in this guide work and they cost nothing. The tradeoff is your time. If you’d rather not spend an hour on this every quarter, that’s the niche tools like Sweep fill — same hunt, automated, with a preview before anything’s deleted. Either approach is fine. The wrong move is dismissing the warning and waiting until your Mac actively breaks.