Not enough space to update macOS: what to clear first

9 September 2026 · 6 min read

A macOS update asks for a good deal more room than the download itself, because it has to store the installer, unpack it, and keep enough of the old system to fall back on if something goes wrong. Software Update will name the figure it wants; treat that as the floor, not the target.

Clear in this order and most Macs get there in under half an hour: emptied Trash everywhere, old macOS installers, iOS device backups, Time Machine local snapshots, then Downloads. Those five account for the majority of stuck updates. What follows is how to do each one and how to tell when the number is not moving for a reason.

How much space it actually wants

The download for a full macOS upgrade is typically 12 to 15 GB. The installation then needs working room on top of that, which is why an update can refuse on a Mac showing more free space than the download size.

Give yourself a comfortable margin rather than scraping past the minimum. An update that runs out of space part way through is a far worse afternoon than one that refuses to start.

A smaller point release needs much less than a full upgrade between major versions, so check which one you are being offered before assuming you need 40 GB.

The five that usually do it

1. Empty every Trash, not just yours. Your Trash, the Trash on any external drive currently attached, and Photos’ Recently Deleted album, which holds items for 30 days on purpose. Mail’s Trash mailbox counts too.

2. Delete old macOS installers. Search Applications for anything named Install macOS. Each one is 12 to 15 GB and there is no reason to keep one after the update it was for. Partially downloaded installers also sit in /Library/Updates.

3. Remove old iPhone and iPad backups. These live in ~/Library/Application Support/MobileSync/Backup and they are the single largest thing on a lot of family Macs, frequently for devices nobody owns any more. Find and delete old iPhone backups on a Mac covers identifying which backup belongs to which device before you delete the wrong one.

4. Thin Time Machine local snapshots. macOS keeps hourly snapshots of your data on the internal drive so you can restore without the backup disk attached. Run tmutil listlocalsnapshots /. If it prints a list, there is space tied up. The safe way to release some is:

sudo tmutil thinlocalsnapshots / 21474836480 4

That asks macOS to free about 20 GB of snapshot space at the highest urgency. Time Machine local snapshots covers what you lose by doing it, which is less than people fear but is not nothing.

5. Go through Downloads. Disk images, installers and archives collect there for years, and they are mostly re-downloadable. Tidying the Downloads folder without losing anything covers doing it without discarding the one thing you needed.

Where to look after that

If you are still short, work down from the biggest measurable items rather than deleting hopefully.

In Terminal, sudo du -xhd 1 /System/Volumes/Data | sort -h ranks the top level of the volume your files live on, then repeat one level down on the largest line. Permission errors along the way are normal.

The usual next four:

• Other user accounts. sudo du -shx /Users/*. On a shared Mac this is often the whole answer, and it is invisible from your account in Finder.
• The Photos library, especially if iCloud Photos is off and every original is stored locally. The Photos library is taking up space covers what is inside it.
• Developer data, if the Mac has Xcode or containers on it. DerivedData, simulator runtimes and disk images are gigabytes each and rebuild themselves.
• Virtual machine images and other APFS volumes in the same container. Run diskutil apfs list and look at every volume, not just Macintosh HD.

If you want that laid out as one list rather than assembled command by command, Crumb audits the whole Mac read-only: System Data broken into its parts, plus local snapshots, iOS backups and a per-account view of a shared machine. It reclaims by category with the total shown before you commit, and nothing is removed until you approve the plan. The audit and one full cleanup are free, which is enough to get an update unstuck.

When the number will not move

You delete 30 GB and the free space figure barely changes. Three explanations cover nearly every case.

It is purgeable, not free. Select the startup disk in Finder and press Command-I. If the Available line reads something like “48 GB available (22 GB purgeable)”, macOS is counting space it intends to reclaim later. Installers are among the programs that refuse to trust that figure and want real free space. Purgeable space on a Mac covers how to make it release.

A process is still holding the deleted files. If an app had a file open when it was deleted, the space stays allocated until that process quits. sudo lsof +L1 shows them; a restart clears the lot.

The storage bar is stale. System Settings, General, Storage recalculates in the background and can be an hour behind. df -h /System/Volumes/Data is the honest live number.

The practical move after a big clearance is simply to restart, then check again before deleting anything else.

If you still cannot get there

Some options that people reach for do not work, and it saves time to know which.

An external drive will not help directly. The update installs to the startup volume, so free space elsewhere does not count. What an external drive is good for is moving your own large files off temporarily: a Photos library, a video project, an archive folder. Move them, run the update, move back what you want.

Reinstalling macOS to reclaim space is not a plan. It does not free your data, and it takes longer than the update you were trying to run.

If the Mac needs a clearance like this every few months, the underlying problem is capacity rather than housekeeping, and it is worth reading it as information rather than a chore.

After the update

Two things to do once it has finished, because both free space back:

1. Delete the installer, if the update left one in Applications.
2. Wait a day, then check the storage figure again. macOS retains some update files for a period afterwards and clears them on its own.

If you turned off anything to make room, such as local snapshots or Time Machine, turn it back on. A decision made under pressure is how a Mac ends up with no backup for a year.

Questions

Software Update says there is not enough space but Finder says there is plenty. Check how much of that free space is purgeable, and check that you are reading the data volume rather than the sealed system volume. df -h /System/Volumes/Data gives the number the installer is working from.

Can I download the installer to an external drive? You can keep a full installer there, but the installation still needs room on the startup volume to unpack and run, so it only solves part of the problem.

Is it safe to delete the Time Machine local snapshots? Yes, in the sense that the real backups on your backup disk are untouched. What you give up is restoring a recent version of a file without that disk attached.

Does clearing caches help? A little, and less than people expect. They are usually a few gigabytes and they come back within days of ordinary use. Do the five items above first, then look at caches only if you are still short.