How much space you need
Apple does not publish one fixed number, because it depends on your Mac and the version you start from. The update itself tells you: if there is not enough room, Software Update or the installer says how much more storage it needs.
As a rule of thumb:
- Minor updates (for example 26.1 to 26.2) usually need a few gigabytes.
- Major upgrades (for example macOS 26 to 27) download an installer of well over 10 GB and need extra room to unpack and install it. Plan for 30 to 40 GB of free space.
More is better. A Mac that installs an upgrade with only a few gigabytes to spare also has little room for swap and caches afterwards, and feels slow in the days after. The guide on how much free space a Mac needs goes into the reasons.
Check what you have
Choose Apple menu > System Settings, then General, then Storage. The bar shows used and available space. Give it a minute: the categories fill in slowly.
Finder’s Get Info on your startup disk may show a larger “Available” figure. It includes purgeable space, mostly Time Machine local snapshots and iCloud files macOS can remove when it needs room. The installer can often use that space, but not always right away, so the number in Storage settings is the safer one to plan with. See purgeable space for the details.
Back up first
Before you clear space and before any major upgrade, make a backup. A Time Machine backup to an external drive does not need space on your Mac.
A fresh backup is also a safety net for the cleanup itself: if you move something to the Trash by mistake and empty it, you can still restore it from the backup.
Quick wins, in order
Work through these from the top and check the free space after each step. Most Macs reach the target in the first four.
1. Empty the Trash
Items in the Trash still use their full space. Open it, look through it, then choose Finder > Empty Trash. This is the step that frees the space, and the one that cannot be undone.
2. Restart
A restart clears swap files and many temporary files. On a Mac that has been running for weeks, that can be several gigabytes.
3. Clear out Downloads
Sort Downloads by size. Disk images (.dmg), installer packages
(.pkg) and archives (.zip) you have already installed or unpacked
can go. You can download them again if you need them.
4. Use the recommendations in Storage settings
Storage settings offers Store in iCloud, Optimize Storage and Empty Trash automatically. Below them, the Info button next to Documents opens Large Files, a list of your biggest files.
5. Free up cloud downloads
Files in iCloud Drive, Dropbox, Google Drive or OneDrive that you have downloaded take full space on your Mac. Control-click a large folder in Finder and choose Remove Download: the files stay in the cloud and download again when you open them. With Optimize Mac Storage turned on, macOS does this for iCloud Drive on its own when space runs low.
6. Move big files you rarely use
Old video projects, photo exports and virtual machines are good candidates for an external drive. Copy them, check that the copy opens, then move the originals to the Trash.
7. Remove old device backups and caches
An old iPhone backup can be 50 GB on its own, and app caches are often several gigabytes. Both have their own guides: iPhone backups and deleting caches. Developers can usually gain the most from Xcode and package manager caches.
What not to delete in a hurry
Also leave Time Machine local snapshots to macOS unless the installer still comes up short after everything above. You can see them with this command, which only lists:
~ % tmutil listlocalsnapshots / Snapshots for disk /: com.apple.TimeMachine.2026-10-29-213045.local
macOS removes them on its own after about a day, or sooner when it needs the space. More in Time Machine local snapshots.
Run the update
Use Software Update in System Settings > General. Apple notes that it can use less storage to download and install updates than other methods, such as downloading the full installer app.
Keep the Mac plugged in, and leave the free space alone while it installs: do not start large downloads or copy big files to the Mac during the upgrade.
After the update
Check Storage settings again a day later. Some space often comes back on its own as macOS cleans up after the update. If you downloaded the full installer app (such as “Install macOS” in Applications) and it is still there after the upgrade, you can move it to the Trash.
Then empty the Trash once you are sure you do not need anything from it.
