How Much Storage Needed for iOS 15.2.1 Update?

iOS, MacOS, or iTunes usually informs the user if there isn't enough free storage on an iPhone to install an update. There are different packages for different iPhone models, along with different free space requirements. So it's kind of hard to give any solid numbers.

For the 15.2.1 incremental update from 15.2 via Wi-Fi, my iPhone 7 came up with a message that at least 1.7 GB was needed. Not sure how much is needed when there's a full update, but Lawrence's 5 GB estimate is probably close to it. But for the update via my Mac, it was a full installation that uses the computer's storage to do a lot of the unpacking, and needed about 950 MB (which I didn't have). I ended up backing up, restoring to factory settings (which installed 15.2.1 as if it were a brand new device), and then restored my data from my backup.

But if you have an iPhone 6 Plus (says that at the bottom of your original post), there is no 15.2.1 update.

That depends on what you are updating from, so the “information” would have to be a spreadsheet with a row for each previous version that you are updating from. Or a blanket statement, like 5 GB, which is the storage required for an over-the-air update to any version of iOS 15 from any version lower than iOS 15. iOS 15.2 to iOS 15.2.1 only requires about 100 MB, however; 15.1 to 15.2.1 around 1 GB, as another example. If you try to update and you don’t have enough storage the update screen will say you don’t have enough storage.

But 5GB is a “safe” answer for all updates.

CityGuy7 wrote:

Thanks - this is helpful!

“like 5 GB, which is the storage required for an over-the-air update to any version of iOS 15 from any version lower than iOS 15. iOS 15.2 to iOS 15.2.1”

Full over the air updates on an iPhone alone require a lot of free space to unpack everything. And even then there are risks.

I prefer to do updates through a computer, which always does it as a full installation rather than incrementally. And it will require a backup to the computer so that there's a way to recover if the installation is corrupted.