What's Taking Up Space on My Mac? How to Find Out Fast

A practical guide · 5 methods compared

Your Mac says it's "almost full" but Apple's storage meter gives you vague categories like "System Data: 40 GB." Here's how to actually see what's eating your disk — from Apple's built-in tools to visual disk analyzers.

TL;DR

Built-in (basic): Apple menu → About This Mac → Storage
Built-in (detailed): du -sh * in Terminal
Best free visual tool: Disk Inventory X or GrandPerspective
Best paid: DaisyDisk ($10) or FileForge ($14.99 — analysis + cleanup in one)

Method 1: Apple's Storage meter (basic)

Apple menu → About This Mac → Storage (pre-Ventura) or System Settings → General → Storage (Ventura+)
Shows broad categories: Apps, Documents, iCloud, System Data, Other
Recommends system actions: "Optimize Storage," "Empty Trash automatically"

Limitation: "System Data" is a black box. Usually 20–60 GB and mostly uninformative.

Method 2: Terminal `du` command (free, technical)

du -sh ~/* 2>/dev/null | sort -hr | head -20

Lists your top 20 biggest home-folder items by size
Works on any macOS version
du -sh ~/Library/* to drill into the Library

Limitation: no visualization; requires Terminal comfort.

Method 3: GrandPerspective or Disk Inventory X (free)

Both use treemap visualization: each file becomes a rectangle sized by file size.

GrandPerspective — simpler, slightly better performance
Disk Inventory X — classic, hasn't been updated in years but still works
Click any rectangle to see the file path

Limitation: read-only — no cleanup actions.

Method 4: DaisyDisk ($10)

Beautiful radial chart (not treemap)
Drag files out of the chart to delete
Very polished UI

Cons: only visualization — no duplicate detection, no ghost files, no bulk cleanup.

Method 5: FileForge ($9.99 launch / $14.99)

FileForge combines disk analysis with the cleanup actions most users actually want:

Disk Analyzer with treemap + drill-down
Dashboard showing top categories + largest directories at a glance
Smart Cleanup for caches/logs/temp (1-click)
Ghost Files detection for leftover data from uninstalled apps
Duplicate Finder for duplicate photos/documents

One tool instead of juggling DaisyDisk + AppCleaner + dupeGuru. Try FileForge.

What's actually in "System Data"?

For most users, System Data breaks down roughly as:

Caches: 5–15 GB (safely removable — FileForge's Smart Cleanup handles this)
Xcode Derived Data: 10–40 GB if you're a developer
Old iOS backups: 2–30 GB (check in Finder under your device)
Time Machine local snapshots: 5–20 GB (macOS manages these)
Mail downloads: 1–5 GB (old attachments)
Podcast/Music downloads: variable
Genuine "system" files: 15–25 GB (macOS itself)

FAQ

Why is my Mac "almost full" if my files only add up to half the drive?

macOS writes snapshots, caches, and temporary files that don't show in Finder. The built-in Storage panel's "Other" category is where this hides.

Can I safely delete files in `~/Library`?

Some, but be careful. Safe: ~/Library/Caches, ~/Library/Logs. Risky: ~/Library/Application Support (contains your app data), ~/Library/Preferences (app settings). FileForge's Smart Cleanup only touches the safe subfolders.

How much space should I keep free?

macOS recommends keeping at least 10% of your drive free for swap and temporary files. On a 500 GB SSD, aim for 50 GB free minimum.

Does emptying Trash really free up space?

Yes, but only after you confirm. Until then, Trash counts toward used space.

Conclusion

Start with Apple's built-in Storage meter for the overview, then use a treemap tool (GrandPerspective is free) to see actual file-level detail. If you want one tool that does analysis + duplicate detection + ghost file cleanup, FileForge is worth the $14.99.