The MacBook Air M2 starts at 256 GB of storage, and a Mac with a Photos library, a few apps and a Downloads folder reaches Startup disk almost full without any warning. Apple's page on freeing up storage says to check the storage in System Settings, General, Storage, where a colored bar shows what uses the space and each category has recommendations.
The checks in more detail
The key ones are Store in iCloud, which moves Desktop and Documents to iCloud Drive and keeps recent files on the Mac, Optimize Storage, which removes watched TV shows and old mail attachments, and Empty Trash Automatically. Remember that a file moved to the Trash still takes space until the Trash is emptied. The categories System Data and Other can be large, and a restart plus a macOS update shrinks them. Large files in Downloads, old iOS backups in Finder and unused apps are common culprits, and the Documents list in Storage sorts by size.
An external SSD is the cheap route for large video and photo libraries, and the Air's two Thunderbolt ports are fast enough for editing from one. After deleting, Storage can take a minute to update, and the Photos library, Mail and iCloud Drive keep local copies that Optimize Storage manages, so check again after a restart. A common surprise is local Time Machine snapshots that hold space; they are released automatically when needed but can show as System Data. Consider turning on iCloud Drive's Optimize Mac Storage in System Settings, your name, iCloud, Drive, which keeps only recently used files on the Mac and leaves the rest in iCloud; the files still appear in Finder and download when you open them.
This is the quickest way to reclaim tens of gigabytes without deleting anything.
Differential
Likely causes of “Apple MacBook Air (M2) storage is full or nearly full”, and how to tell them apart
- 1
A Photos library and videos
What separates it Photos and Movies take most of the space
How to confirm Store in iCloud, or move the library to an external SSD
- 2
The Trash not emptied
What separates it Deleted files still occupy space
How to confirm Empty the Trash, or turn on Empty Trash Automatically
- 3
Old backups and downloads
What separates it Documents and Downloads are huge
How to confirm Sort by size and delete what you do not need
- 4
A large System Data figure
What separates it System Data shows tens of gigabytes
How to confirm Restart and update macOS; remove old caches and backups
- 5
A small 256 GB drive
What separates it The Mac is always almost full
How to confirm Use an external SSD for large libraries
Before you touch a setting
Record this first — changing settings destroys the evidence
- The storage bar's largest categories
- The size of the Photos library
- Whether iCloud storage is available
- The macOS version
Try in this order
0 of 8 completedOpen Storage
ReversibleSystem Settings, General, Storage.
Follow the recommendations
ReversibleStore in iCloud, Optimize Storage and Empty Trash Automatically.
Empty the Trash
ReversibleControl-click the Trash and choose Empty.
Sort Documents by size
ReversibleIn Storage, Documents, delete or move large files.
Remove old iOS backups
ReversibleIn Finder, Manage Backups.
Move large libraries to an external SSD
ReversibleUse a Thunderbolt drive.
Restart and check Storage again
ReversibleThe figures update after a restart.
Check for Time Machine snapshots
ReversibleThey show as System Data and are released when space is needed.
Model-specific
What is true of this model and not of its siblings
- A small base drive
- 256 GB fills quickly.
- Trash
- Deleted files take space until it is emptied.
- Snapshots
- Local snapshots occupy System Data.
- Mail downloads
- Mail keeps local copies of attachments.
Stop boundary
When this stops being a self-service repair
- !If storage looks full but is not, restart and reindex, then contact Apple Support
- !If System Data stays huge after a restart, ask Apple
- !Back up before deleting large folders
Evidence ledger
Sources behind this answer
Exact questions
Common questions
How much storage does the M2 Air have?+
256 GB at the start, up to 2 TB.
Does emptying the Trash free space?+
Yes, only then.
What is System Data?+
Caches and system files.
Can I use an external drive?+
Yes, with its Thunderbolt ports.
Why does Storage not update?+
Restart and wait.
What are Time Machine snapshots?+
Local backup copies.