Search for Golden Gate's storage requirements and you'll find numbers anywhere from 17 GB to 50 GB. The reason for the spread is simple: Apple hasn't published an official figure, so every guide is guessing from a different angle.

Here's the working answer, why it's higher than the installer size, and how to get there on a Mac that's already tight on space.

The short answer

Aim for 40 GB free before you start. If you have 60 GB free, stop reading and go upgrade.

The installer itself is around 17–18 GB. The installer will refuse to start below roughly 30–35 GB, and upgrades that squeeze past that threshold are the ones that stall at "Preparing" or fail and roll back. On a 256 GB Mac, 40 GB is also close to the 10–15% free space macOS wants for normal operation anyway.

Why the installer size isn't the number that matters

An upgrade needs space for several things at once, and most of them aren't visible in Software Update.

  1. The download. Around 17–18 GB for the full installer. Software Update's over-the-air package is usually smaller, because it only fetches what's needed to upgrade your existing system.
  2. Unpacking and staging. The installer expands its payload and builds the new system volume alongside the current one. Your old system stays intact until the new one boots successfully, so for a while both exist.
  3. Working room after the upgrade. macOS needs space for swap, caches, and APFS snapshots as soon as it starts. A Mac that finishes the install with 3 GB left will feel broken even if nothing is wrong.
  4. On-device AI models. Apple Intelligence downloads its models after the upgrade, not before. That space gets used in the first hours or days, often while you're already wondering where your storage went.

If you download the full installer instead of using Software Update, for example to keep a bootable copy, count the installer twice: once as the downloaded app, once during installation. Delete it afterward.

Check how much space you really have

Finder and System Settings both report "available" space that includes purgeable data: iCloud files that can be evicted, caches macOS can clear, and local Time Machine snapshots. That space usually becomes free on demand. The installer doesn't always agree, which is how you end up with Finder saying 45 GB available and the installer saying there isn't enough.

To see the difference, open Terminal:

df -h /System/Volumes/Data

The Avail column is space that's free right now, without purging anything. Compare it with what Finder shows. If Finder's number is much higher, the gap is purgeable data.

Local Time Machine snapshots are the most common hidden consumer. List them:

tmutil listlocalsnapshots /

If you see a long list and your external backup is current, you can ask macOS to thin them: 

tmutil thinlocalsnapshots / 999999999999 4

The large number is the amount to reclaim in bytes (effectively "as much as possible"), and 4 is the urgency level. macOS removes snapshots it considers safe to remove. Your backups on the external drive aren't touched.

Safe ways to free up 20 GB or more

Start with the biggest items, not the tidiest ones. Deleting 400 small files feels productive and usually recovers less than one forgotten VM image.

Old iPhone and iPad backups. Local device backups can take tens of gigabytes each. Check how much space they use: 

du -sh ~/Library/Application\ Support/MobileSync/Backup

Manage them from Finder: select your device, go to the General tab, and click Manage Backups. If your devices back up to iCloud, old local backups are often safe to delete.

Old macOS installers. Look in Applications for Install macOS Tahoe.app or older versions. Each is well over 10 GB.

Virtual machines and container images. Parallels, VMware Fusion, UTM, and Docker all keep large disk images. Docker in particular grows quietly: 

docker system df
docker system prune

Read what prune is going to remove before confirming. For VMs, delete machines you don't use rather than trying to shrink the ones you do.

Developer leftovers. If you've ever installed Xcode, these are usually the jackpot: 

du -sh ~/Library/Developer/Xcode/DerivedData
xcrun simctl delete unavailable

DerivedData is a build cache and is safe to delete; Xcode rebuilds it. The second command removes simulators for runtimes that are no longer installed. If you use Homebrew, brew cleanup removes old package versions and cached downloads.

Photos and Messages. In Photos, go to Settings > iCloud and turn on Optimize Mac Storage if your library lives in iCloud. Full-resolution originals stay in iCloud and download on demand. In Messages, go to Settings > General and change Keep Messages from Forever to one year. This deletes older messages and attachments from this Mac, and from other devices if Messages in iCloud is on, so be sure that's what you want.

Large files you forgot about. System Settings > General > Storage lists categories with an info button next to each. The Documents view sorts files by size and shows old downloads and unsupported apps. It's the quickest way to find a 12 GB screen recording from 2023.

What not to do

  • Don't delete anything inside `/System` or `/Library` because a blog listed the folder. Most of what "System Data" shows is snapshots, caches, swap, and app support files. Deleting the wrong thing there causes problems that surface after the upgrade, when they're hardest to diagnose.
  • Don't clear `~/Library/Caches` wholesale right before upgrading. It rarely frees much, apps rebuild caches immediately, and some apps lose state.
  • Don't move your home folder or Photos library to an external drive just to pass the check. If that drive disconnects during or after the upgrade, you'll spend the first day fixing permissions and library paths.
  • Don't count on the installer to clean up after itself. Check again after upgrading.

After the upgrade: where the space goes

It's normal to lose some space in the first few days, and then to get part of it back.

The new system and Apple Intelligence models take their share. Apple lists about 7 GB of storage for Apple Intelligence, but many Golden Gate users report much larger figures under System Settings > General > Storage > macOS, and there's no supported way to delete the models while keeping the system intact. Turning Apple Intelligence off may or may not return that space, and reports are mixed. At the same time, the upgrade often leaves behind the installer package, caches from Tahoe that Golden Gate no longer reads, and snapshots created during the transition. Most of that clears on its own.

Check storage again about a week after upgrading. If System Data is still dramatically larger than before, list local snapshots again with tmutil listlocalsnapshots /, and check whether the full installer app is still sitting in Applications.

Quick checklist

  • df -h /System/Volumes/Data shows at least 40 GB available.
  • Recent backup on an external drive or SMB share.
  • Old device backups, installers, and VM images reviewed.
  • Local snapshots thinned if the list was long.
  • A reminder set to check storage again a week after upgrading.

If you're still short after all of that, the real problem isn't Golden Gate. It's a 256 GB drive doing a 512 GB job, and it's worth fixing on its own terms before the next major release makes the same demand again.