In short
- Start with what you can't lose: the Trash, used installers in Downloads, and browser caches.
- Then check old iPhone backups, apps you no longer use, and large files you haven't opened in months.
- Leave
/System,/privateand~/Library/Application Supportalone. - If System Data is the largest category, the space is in caches, app data and backups.
First, see where the space went
Open System Settings → General → Storage. The bar at the top shows your categories. If System Data is the largest, the space is in caches, app data and backups that macOS doesn't break down. Here is what System Data contains.
What to remove, in order of risk
No risk
- Empty the Trash. Right-click the Trash in the Dock and choose Empty Trash.
- Delete installers in Downloads. Files ending in
.dmg,.pkgor.zipthat you've already installed from. - Clear browser caches. In Chrome: Settings → Privacy and security → Delete browsing data → Cached images and files. Safari and Firefox have the same option. More on clearing caches.
- Restart. This clears temporary files and swap space.
Check first
- Old iPhone and iPad backups. In Finder, select your device, then Manage Backups. A backup can be 10 GB or more. Keep it unless the device also backs up to iCloud.
- Apps you no longer use. Drag them from Applications to the Trash. Their data stays behind in
~/Library. - Large files you haven't opened in months. In Finder, search This Mac, add the File Size filter (under Other), and sort by size.
- Offline downloads in apps. Music, podcasts and video apps keep downloads you may have forgotten. Remove them inside each app.
Leave alone
- Anything in
/Systemor/private. macOS manages these. ~/Library/Application Supportas a whole. It holds app settings, message history and licenses.- Your Photos library, unless you've moved it to iCloud or an external drive on purpose.
If macOS says the disk is full but shows free space, some of that space is purgeable: macOS frees it when needed. Restarting can release some of it.
The quicker way
StorageJanitor does the steps above in one scan. It totals what is safe to delete right now, then lists the rest as suggestions: device backups, large old files, unused apps, installers and data left by deleted apps. Each has a size and a reason.
Questions people ask
What should I delete first when my Mac storage is full?
Start with things you can't lose: empty the Trash, delete installers in Downloads, and clear browser caches. Then look at old iPhone backups, apps you no longer use, and large files you haven't opened in months.
Why is my Mac storage full when I have few files?
The space is usually in places Finder doesn't show by default: app caches, app data, device backups and local snapshots, most of which macOS reports as System Data.
How much free space should a Mac have?
There is no official figure. Keeping around 10% of the disk free leaves macOS room for updates, swap space and temporary files.
What is purgeable space?
Purgeable space holds files macOS can remove on its own when room is needed, such as local snapshots and files also stored in iCloud. It already counts toward the space available to you.
Is it safe to use a Mac cleaner app?
It depends on what the app removes. Prefer one that shows every item before removing it, explains why each is safe, and moves anything you might want to the Trash instead of deleting it.