How to free up space for a macOS update

When an update won’t install because there isn’t enough storage, macOS usually tells you how much more space it needs. Major upgrades can need tens of gigabytes free while they install, even though much less stays in use afterwards.

Check how much you have

Open System Settings › General › Storage. The bar at the top shows what’s in use. Some installers ignore purgeable space, so if you’re close to the limit, free up real space rather than counting on macOS to clear it.

Quick wins, biggest first

Empty the Trash, and look in your Downloads folder for old installers and disk images (.dmg files).
Delete iPhone and iPad backups you no longer need. In Storage settings, click the ⓘ button next to iOS Files.
Remove apps and games you don’t use. Games and creative apps can take tens of gigabytes each.
Delete local Time Machine snapshots, if you use Time Machine.
Move large photo, video or music libraries to an external drive.

If you develop software

Xcode simulators and build data add up quickly. This command removes simulators for iOS versions you no longer have installed:

$ xcrun simctl delete unavailable

You can also delete the contents of ~/Library/Developer/Xcode/DerivedData. Xcode rebuilds it the next time you build a project.

Find the rest with a disk map

If that isn’t enough, scan your startup disk with OpenDisk. The biggest folders are the widest slices of the chart, so you can see in seconds where the space went. Collect what you don’t need, check the total, and remove it all in one step.

After the update

Leave some room. macOS needs free space for virtual memory and the next update, so try to keep at least 10 to 15 percent of your disk free.