Startup disk almost full on your Mac: what to clear first

When your Mac warns that the startup disk is almost full, start in System Settings > General > Storage. It shows what is taking the space and offers a few one-click fixes. After that, the biggest wins are almost always the same: the Downloads folder, old installers, iPhone and iPad backups, large videos, and a Trash you forgot to empty.

Work through those in order and you will usually free plenty of room without touching anything risky. This post walks through each one, explains what not to delete, and covers why a nearly full disk makes a Mac feel slow.

See what is using the space

Open System Settings and go to General > Storage. At the top is a bar split into colored sections, one for each kind of data, with the free space at the end. Give it a minute: on a full disk it can take a while to finish counting.

Below the bar is a list of categories, such as Applications, Documents, Photos, Mail, Messages, iOS Files, Trash, macOS and System Data. Each has a size, and most have an info button that opens a list you can sort and delete from. In recent versions of macOS, the info button next to Documents is especially useful, because it lists your largest files and the contents of Downloads in one place.

For a quick look at free space any time, open a Finder window and choose View > Show Status Bar. The bar at the bottom of the window shows how much space is available.

Start with the recommendations

Near the top of the Storage pane, macOS offers a few recommendations. Read each one before you turn it on, because they work quite differently.

• Store in iCloud moves files to iCloud and keeps only recent ones on the Mac when space is needed. It can cover Desktop and Documents, Photos and Messages. It only helps if you have enough iCloud storage, and older files then download when you open them, which needs a connection.
• Optimize Storage removes Apple TV movies and shows you have already watched, and keeps only recent email attachments in Mail on the Mac. You can download any of them again.
• Empty Trash Automatically erases items that have been in the Trash for more than 30 days. This one is a good default for almost everyone.

If you would rather choose by hand, skip the recommendations and work through the list below.

The usual culprits

Downloads

The Downloads folder quietly collects everything: installers, PDFs you read once, zip files you already opened, videos from a chat. To find the big ones, open Downloads in Finder, choose View > as List, then click the Size column header. For folders to show a size, choose View > Show View Options and tick "Calculate all sizes".

Anything you can download again, or have already opened and filed elsewhere, can go.

Old installers and disk images

When you install an app from a download, the disk image (a .dmg file) or installer package (a .pkg file) is left behind in Downloads. Once the app is in Applications, you no longer need it. Also check Applications for an "Install macOS" app that you downloaded and never ran, or kept for later. A full macOS installer takes many gigabytes, and you can always download it again from Apple.

iPhone and iPad backups

If you have ever backed up an iPhone or iPad to your Mac, those backups can be very large, and old ones stay until you delete them. In the Storage pane, click the info button next to iOS Files to see device backups and software update files, and delete the ones you no longer need. You can also connect the device, select it in the Finder sidebar, and click Manage Backups.

Keep the newest backup of any device you still use, unless it is backed up to iCloud instead.

Video, photos and screen recordings

Video is the largest kind of file most people own. Screen recordings land on the Desktop by default and are easy to forget. To hunt for big files anywhere on the Mac, press Command and F in Finder, choose This Mac, then change the Kind menu to Other and pick File Size. Set it to "is greater than" one gigabyte and see what turns up.

If you use iCloud Photos, Photos > Settings > iCloud has an Optimize Mac Storage option that keeps smaller versions on the Mac and the originals in iCloud. Messages can also hold years of photos and videos. In Messages > Settings > General, the Keep messages menu decides how long they stay.

Caches and System Data

System Data is the category people ask about most, because it is large and hard to inspect. It includes caches, logs, temporary files and local Time Machine snapshots. Much of it is managed by macOS, and some of it shrinks on its own after a restart or when space runs low.

It is tempting to go into the Library folder and delete caches by hand. Mostly that just makes apps rebuild them, and deleting the wrong folder can break an app or lose settings. Leave System Data alone unless you know exactly what a file is. Be wary of cleanup tools that promise to free huge amounts of space by sweeping it out.

The Trash

Files you delete in Finder still take up space until the Trash is emptied. Choose Finder > Empty Trash, or press Shift, Command and Delete. Photos has its own Recently Deleted album, where deleted pictures wait for around 30 days. Open it from the sidebar to delete them sooner.

A safe cleanup, step by step

1. Make sure you have a backup. Before you delete anything in bulk, check that Time Machine or another backup is up to date. If you don't have one yet, see how to set up Time Machine.
2. Empty the Trash. It is the fastest win and needs no decisions.
3. Sort Downloads by size and delete what you can get again.
4. Delete leftover installers, .dmg and .pkg files and old "Install macOS" apps.
5. Remove old device backups from iOS Files.
6. Move big videos and archives to an external drive if you want to keep them but don't need them every day.
7. Restart the Mac. This clears some temporary files and lets macOS tidy up.
8. Check the Storage pane again to see where you stand.

Why a full disk slows a Mac

A Mac uses free space on the startup disk all the time, not just for your files.

• Memory. When apps need more memory than the Mac has, macOS moves some of it into swap files on the startup disk. With almost no free space there is little room for that, and the whole Mac can start to stall.
• Caches and temporary files. Apps write working files as they go. Without room, they slow down, refuse to save, or quit unexpectedly.
• Updates. macOS updates need space to download and unpack before they install. On a nearly full disk, Software Update may tell you there isn't enough room, which leaves security fixes waiting.
• Syncing. Photos, Mail and iCloud Drive may pause syncing when the disk is short of space.

Some of the space in the Storage pane may be described as purgeable. That is data macOS can remove by itself when it needs room, such as local Time Machine snapshots or files already stored in iCloud. It is not a problem, but it means the numbers can shift a little between one look and the next.

A heads-up before it gets tight

The best time to clean up is before the warning, when you can do it calmly. A glance at the Storage pane once a week, as part of a weekly Mac care routine, catches most of it early. In Notchpals, the startup disk is one of the things the Tech care area keeps watch over. With Juice or Gumdrop in your crew, a disk that drops below 10 percent free gets a visit from the notch suggesting a tidy, at most once a week.

JuiceSo many downloads, so little room. A tragedy. Let some of them go.

Press Done once you have made some room. Choose Later and it looks in once more after 20 minutes, provided the disk is still that full. Notchpals only reads how much space is free, never which files are taking it, and that figure stays on your Mac. The same character also speaks up when your battery runs low or a week passes without a restart. If you suspect the second one, here is how to check how long your Mac has been on.