How big is macOS 27, and how much free space do you need?
Short answer. Apple doesn't publish how much free space you need to upgrade to macOS 27 Golden Gate. The upgrade from macOS 26 Tahoe was a 30.8 GB download, and the 27.2 update is 21.8 GB. Once installed, macOS 27 itself takes roughly 28 GB, and Apple Intelligence adds up to 14 GB by Apple's figure (22.19 GB on our MacBook Air M4). An upgrade needs much more room while it runs than the download size, so free up space before you start, not halfway through.
The numbers
| What | Size | Source |
|---|---|---|
| Upgrade from macOS 26 to 27.0, via Software Update | 30.8 GB download | Eclectic Light, 14 September 2026 |
| Update to 27.0.1 | about 3.3 GB download | Eclectic Light, 28 September 2026 |
| Update to 27.2 (there was no 27.1 for Macs) | 21.8 GB download | Eclectic Light, 26 October 2026 |
| macOS 27 itself, once installed | roughly 28 GB (an estimate, not a measurement) | Eclectic Light, 20 September 2026 |
| Apple Intelligence models | up to 14 GB (M3 or later with 12 GB of memory or more), up to 8 GB on other Macs | Apple |
| Apple Intelligence on our MacBook Air M4 | 22.19 GB in Storage settings | Our measurement, 6 October 2026 |
| Used space during and after the upgrade, on one Mac mini | about 150 GB higher at its peak, then about 30 GB higher a day later | Eclectic Light, 18 September 2026 |
Download sizes depend on which version you're coming from and which Mac you have, so treat them as a guide. Software Update shows the exact size for your Mac before it starts.
Which Macs can run macOS 27
Only Macs with Apple silicon: every Mac with an M1 chip or later, plus the MacBook Neo. No Intel Mac can install it (Apple). Intel Macs stay on macOS 26 Tahoe or earlier.
Why the upgrade needs more than the download
The download is only part of it. While an upgrade runs, your Mac also needs room to:
- Unpack and prepare the update next to the macOS you're still running.
- Keep a snapshot. Apple says macOS saves a snapshot before installing any macOS update (Apple). It holds the old system until it's no longer needed.
- Download Apple Intelligence models after the upgrade, if your Mac supports them.
That's why used space can jump far above the download size and then drop again a day or two later. Apple doesn't give a figure to aim for. Our rule of thumb is to have at least twice the download size free before you start (about 60 GB for the upgrade from macOS 26), and more if you can. If there isn't enough room, the installer says so.
How to check your free space
- Choose Apple menu > System Settings, then General > Storage.
- Wait for the bar at the top to finish loading. The free space is shown next to it.
Finder and Storage settings may count purgeable space (space macOS can free by itself) differently. If the numbers disagree, what purgeable space is explains why, and how to see it in Disk Utility.
Not enough space to install?
Apple's advice is simply to free up storage space (Apple). It also says that starting your Mac in safe mode clears some system caches, which can give you enough room to install a macOS update (Apple).
The quickest safe wins, roughly in order:
- Empty the Trash, and the Recently Deleted album in Photos.
- Delete old iPhone and iPad backups you no longer need. Each one can be tens of gigabytes: how to delete old iPhone backups.
- Clear app and browser caches. They're safe to remove and come back slowly: how to clear the cache on a Mac.
- Remove developer leftovers if you use Xcode, Docker or npm: freeing up developer storage.
- Move or delete large files you've forgotten about: how to find large files.
The full checklist, with how much each step usually frees, is in how to free up space on your Mac. Don't delete system folders by hand to make room. They're protected, and what's in them is what the upgrade needs.
After the upgrade
- Give it a day or two before you judge your free space. The snapshot and staged update files are removed once macOS no longer needs them.
- If System Data stays much larger, see what System Data on Mac is, and why it's so large.
- If the macOS line in Storage settings looks big, click its (i). Apple Intelligence is listed there in macOS 27: how much space Apple Intelligence takes.
DiskFox, which we make, keeps a dated history of your storage. After an update it shows what grew and by how much, and labels growth soon after a macOS update as its Likely cause, so you can tell the update's own files apart from something else filling your disk. It's a one-time purchase with a 14-day free trial; see the Mac storage tracker page.