Need to free up space on a Mac? If your Mac keeps saying the startup disk is almost full, you are not alone. This is especially common on older MacBook Air models and 256GB iMacs, because many were sold with small internal drives that fill up quickly with photos, videos, iPhone backups, Mail attachments and old downloads.
The good news: you often do not need a new Mac. You need to find what is actually taking the space, move the right things, and avoid deleting anything important in a panic.
First: check how much space is really available
On recent versions of macOS:
- Click the Apple menu in the top-left corner.
- Open System Settings.
- Go to General > Storage.
On older versions of macOS, use Apple menu > About This Mac > Storage.
Give the Storage screen a minute to calculate. The categories are useful, but not perfect. In particular, System Data can look mysterious because it includes caches, logs, temporary files, app support files, and other bits macOS does not put neatly into a friendlier category.
How to find large files on a Mac
The quickest win is usually not deleting hundreds of tiny files. It is finding the one forgotten video, installer, backup, or disk image that is quietly taking 20GB.
- Open System Settings > General > Storage.
- Click the Info button next to Documents.
- Look for views such as Large Files, Downloads, and File Browser.
- Sort by Size, largest first.
- If you are not sure what something is, click Show in Finder before deleting it.
Common space-hogs include:
- Old .dmg installer files in Downloads
- iPhone or iPad backups
- Videos exported from iMovie, Zoom, Teams, or screen recordings
- Duplicate photo and video folders
- Old printer/scanner installers
- Large ZIP files you already unpacked
- Virtual machines, developer files, or AI/model downloads if you use specialist software
Clean the Downloads folder
Open Finder, then choose Go > Downloads. Sort by size or date and look for old installers, duplicate downloads, ZIP files, and videos.
Downloads is often the digital equivalent of the kitchen drawer: useful once, then somehow full of mystery cables and receipts from 2017.
Empty the Trash properly
Dragging files to the Trash does not free the space straight away. You need to empty it.
- Click the Trash icon in the Dock.
- Check there is nothing inside that you still need.
- Click Empty.
Only do this when you are sure. Once the Trash is emptied, recovery is not something to rely on.
Check old iPhone and iPad backups
If your Mac has ever backed up an iPhone or iPad, those backups can be enormous.
On newer macOS versions:
- Connect the iPhone or iPad, if needed.
- Open Finder.
- Select the device in the Finder sidebar.
- Click Manage Backups.
- Remove old backups you no longer need.
Do not delete your only current backup unless you are sure your device is backed up somewhere else, such as iCloud.
Move Photos and video libraries carefully
Photos and videos are often the biggest users of space, especially on small-drive MacBook Airs and 256GB iMacs.
If you use Photos, your photo library may be one large file called Photos Library.photoslibrary. Do not go rummaging inside it and deleting random folders. That is how sadness gets a progress bar.
Better options include:
- Turn on iCloud Photos with Optimise Mac Storage, if you are comfortable using iCloud and have enough iCloud storage.
- Move large video projects to an external SSD.
- Export old videos you want to archive, then remove them from the Mac once safely copied.
- Keep at least one backup before moving a Photos library.
Remove apps you no longer use
In System Settings > General > Storage, click the Info button next to Applications. Sort by size and look for large apps you no longer need.
Examples might include old games, duplicate office apps, unused Adobe apps, GarageBand sound libraries, or software for printers you no longer own.
Mail, Messages and attachments
Email and Messages attachments can quietly build up over years.
- In Mail, use Mailbox > Erase Junk Mail and Mailbox > Erase Deleted Items.
- In Storage settings, check whether Messages is using a large amount of space.
- Remove large videos and attachments from conversations you no longer need.
Use iCloud carefully
Apple’s storage recommendations may suggest Store in iCloud or Optimise Storage. These can help, but they are not magic.
Things to remember:
- iCloud storage is separate from Mac storage and may require a paid plan.
- Files may still appear on your Mac but download only when needed.
- If your internet connection is poor, relying heavily on iCloud can be annoying.
- Before making big changes, make sure you understand what is stored locally and what is stored in iCloud.
Use an external SSD for archives
For a MacBook Air or 256GB iMac, an external SSD can be the simplest long-term fix. Move archives, old videos, completed projects, and installers off the internal drive.
A sensible approach is:
- Keep current work on the Mac.
- Move old projects and large media to an external SSD.
- Keep a second backup of anything important.
Do not make an external drive the only copy of your photos, accounts, family videos, or important documents. External drives fail too, because apparently technology enjoys drama.
Be careful with “cleaner” apps
Some Mac cleaner apps are useful, some are unnecessary, and some mostly clean out your wallet. Be very cautious with anything that promises to fix everything in one click.
Avoid deleting:
- Anything inside System or Library unless you know exactly what it is.
- Photos Library contents by hand.
- Random files labelled “cache” if they belong to software you rely on.
- Backups before checking you have another safe copy.
When “System Data” is huge
System Data can include caches, logs, temporary files, app support files, local snapshots, and other behind-the-scenes storage. macOS manages some of this automatically, but it can still grow confusingly large.
If System Data is taking a huge chunk of your drive, the safest first steps are:
- Restart the Mac.
- Install available macOS updates if you have enough space.
- Empty the Trash.
- Check Downloads, large files, iPhone/iPad backups, Photos, Messages, and Mail first.
- If you use Time Machine, check whether local snapshots are contributing to the problem.
There are ways to inspect deeper storage usage, but it is easy to delete the wrong thing if you start poking around in hidden folders.
Quick checklist for a nearly full Mac
- Check System Settings > General > Storage.
- Sort Documents by large files.
- Clear old items from Downloads.
- Delete old iPhone/iPad backups you no longer need.
- Move large video/photo archives to an external SSD.
- Remove unused apps.
- Clear Mail junk and deleted items.
- Empty the Trash.
- Restart the Mac and check storage again.
Need help clearing space safely?
If your MacBook Air or iMac is nearly full and you are not sure what can safely go, I can help you find the large files, explain what is safe to remove, and move important things to a backup or external drive without wrecking your photo library in the process.
If you need Mac support at home in Bournemouth, Poole, Dorset or Wiltshire, book a home visit or ask about remote Mac help.
FAQs about freeing up Mac storage
Why does my MacBook Air run out of storage so quickly?
Many MacBook Air models were sold with 128GB or 256GB drives. Once macOS, apps, photos, iPhone backups and downloads are added, the remaining space can disappear quickly.
Is it safe to delete System Data on a Mac?
Do not randomly delete files from System or Library folders. System Data can include useful caches, logs, app support files and temporary files. Start with large files, Downloads, old backups, apps, Mail and Messages before touching anything hidden.
What is the fastest way to free up space on a Mac?
The fastest safe wins are usually deleting old downloads, removing old iPhone or iPad backups, moving large videos to an external SSD, uninstalling unused large apps and emptying the Trash.