The amount of free space required to upgrade a Mac has increased drastically in the run-up to and since the introduction of apfs-based snapshots in 2016. The amount of required free space had been growing steadily in the HFS+-era of file systems, but as more elements of iOS (like a modern file system) came to the Mac, and as the Mac transitioned to a fully 64-bit operating system, that number escalated and never returned now that the transition away from things like 32-bit apps and kexts is finished.
Sierra (Mac OS X 10.12) had a minimum drive capacity of 8.8 GB but really needed more like 12 GB; however there wasn’t a hard number sanity check that I personally ran into. This was 2016 and the amount of free space required to do an upgrade would increase dramatically. The free space required to upgrade to El Capitan (Mac OS X 10.11) was 8.8 gigabytes as well, with 10GB being recommended. The next few years saw new file systems, new apps, new ways of handling various objects on the file system, backing up snapshots to allow for easier recoverability, etc. This is all great for the end users as problems with upgrades from previous versions seem to all but have disappeared. So we see the following progression of free space requirements:
- High Sierra (macOS 10.13) required 14.3GB in free space to upgrade from previous versions.
- Mojave (macOS 10.14) required 12.5 (El Capitan or later) to 18.5 GB in free space for Yosemite or older.
- Catalina (macOS 10.15) required 18.5 GB of free space to upgrade from previous versions of macOS.
- Big Sur (macOS 11) Sierra or later required 35.5GB or 44.5GB for El Capitan and earlier.
- Monterey (macOS 12) required 26GB and up to 44GB of space.
- Ventura (macOS 13) requires 25GB.
The installers themselves grew some as well in this time frame, although not as drastically:
- El Capitan was 6.2GB on the App Store. https://apps.apple.com/us/app/os-x-el-capitan/id1147835434?mt=12
- The Sierra installer was a little less than 10GB of space when put on a thumb drive to be installed, or 5GB on the App Store. https://apps.apple.com/us/app/macos-sierra/id1127487414?mt=12
- The High Sierra installer was 4.8GB (https://apps.apple.com/us/app/macos-high-sierra/id1246284741?mt=12).
- The Mojave installer is 5.8GB.
- The Monterrey installer was 12.16GB. https://apps.apple.com/us/app/macos-mojave/id1398502828?mt=12
- The Ventura installer is 12.19GB. So the installers haven’t changed all that much. https://apps.apple.com/us/app/macos-ventura/id1638787999?mt=12
The net result is that when doing the last few upgrades, they have required 12+GB for the installer itself (which can be run from a USB drive) and up to 44GB for the installer to do the work it needs to do, so a total of up to about 56GB. Therefore, scoping policies to run an updater without causing undo issues to end users it’s entirely appropriate to make sure they have the amounts of free space indicated per version. Given that drives can be a terabyte in size, this doesn’t seem wildly inappropriate; however, many organizations still buy devices with 256GB drives (thus going from an eighth in the 64GB drive era to a quarter of common drive space required to be free for certain upgrades on smaller drives today). Emptying downloads, trash, and other directories isn’t always possible (the number of people who use those as actual storage is astounding), as is clearing duplicate profiles in Outlook and other apps. Long-term it’s probably cheaper to buy devices with larger drives than have to depot them to get users upgraded or take other tactics.
