Apple has never published a specific gigabyte figure for how much free space any iOS release needs, including iOS 27. What Apple does document, in detail, is what to do when Settings says there is not enough room: use its Recommendations, and know the difference between offloading an app and deleting one, because that difference decides whether you lose anything.
iOS 27 arrives Monday, September 14, as a free update, and the storage prompt is one of the most common ways that day goes wrong, as covered in our recap of everything Apple announced on September 9. Here is exactly what Apple’s support article says to do, and the one number it still will not give you.
Key facts on iOS 27 storage requirements
| Question | Apple’s documented answer |
|---|---|
| How many gigabytes does iOS 27 need? | Apple has not published a figure, for this or any release. |
| Where do I check what is using space? | Settings, then General, then [Device] Storage. |
| What does Offload App do? | “Frees up storage used by the app, but keeps its documents and data.” |
| What does Delete App do? | “Removes the app and its related data.” |
| Do apps removed by the updater come back? | Yes. “After installation is complete, those apps are automatically reinstalled.” |
Why Apple will not give you a number
Apple’s support document “If you need more space for an update on your iPhone, iPad or iPod touch” frames the problem the same way every cycle: “If there isn’t enough space to download and install an update, manage your space with recommendations.” It does not attach a gigabyte figure to that sentence, this cycle or any other. The article is still dated December 5, 2025, with screenshots taken on iOS 26, so the exact Storage screen may shift slightly once iOS 27 ships, though the offload and delete definitions on it are unlikely to change.
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The on-device installer is the only place that number ever appears, at the moment it checks your free space and either proceeds or tells you to clear room. That is a deliberate design, not an oversight Apple forgot to fix, and no published Apple document contradicts it.
Offload versus delete, in Apple’s own words
This is the distinction almost every non-Apple guide gets wrong, and Apple’s own storage page settles it in two short lines. Offloading an app frees the space the app itself takes up while keeping your documents and data in place, so a game keeps your save and a document app keeps your files. Deleting an app removes both the app and its related data. If you are clearing space specifically to install iOS 27, offloading is the documented way to do it without losing anything, and it pairs with a second Apple fact worth knowing before you touch anything: apps the updater itself removes to make room are automatically reinstalled once installation finishes.
What to do when the prompt appears
| Documented step | Where it comes from |
|---|---|
| Open Settings, General, then [Device] Storage | If you need more space for an update |
| Scroll to Recommendations for tailored suggestions | If you need more space for an update |
| Offload apps you are not using rather than deleting them | If you need more space for an update |
| Update from a Mac or PC if space is still short | If you need more space for an update |
| Check device storage against iCloud storage, which are separate | Device storage vs. iCloud storage |
That last row matters because it is a genuinely common mix-up: buying more iCloud storage does not free a single byte on the phone itself, and Apple’s own pages treat the two as separate topics for exactly that reason. If the update route via a computer is the one you end up using, that is also Apple’s documented fallback when an over-the-air install will not fit, the same fallback covered for the iPhone 18 Pro and every other eligible iPhone, back to the iPhone 11 and iPhone SE (2nd generation) floor Apple set for this release. iPhone 18 Pro’s own battery figures are unaffected either way, since a full battery has no bearing on how much free storage the installer finds.
What Apple has not said
Apple has not published a minimum free-space figure for iOS 27, has not said whether the December 2025 storage article will be revised for this release, and has not published a time estimate for how long offloading or deleting apps should take to free enough room. It has also not recommended any third-party cleanup tool, and neither do we. The documented path is Settings, Recommendations, offload over delete, and a computer if none of that clears enough space.
Check Settings, General, iPhone Storage on your own device before Monday, September 14, since that screen, not any article, is the only place that will tell you the actual number that matters for your iPhone.
