Start with the storage chart, not with guesswork
Settings → General → iPhone Storage shows a coloured bar and then every app ranked by size. That ranking is the whole plan: the top five entries almost always account for more space than everything below them combined, and deleting a hundred small things is wasted effort by comparison.
Give the screen thirty seconds to finish calculating before acting on it. The numbers move while it works, and System Data in particular is wildly inaccurate until it settles.
Offload large apps — the biggest win for the least loss
Every app in that list offers Offload App. It removes the application itself but keeps all of its documents and data, leaves the icon on the Home screen with a small cloud badge, and reinstalls everything exactly as it was when you tap it.
Games and streaming apps are the targets. Offloading three or four of them routinely frees ten gigabytes in under a minute, and nothing is lost. This is the single most effective thing on this page.
Downloaded video and music
Netflix, Disney+, YouTube, Spotify and Apple Music all cache downloads that never expire on their own. Each app manages its own downloads in its own settings, and iPhone Storage will show you which one is the offender.
A single downloaded season can be several gigabytes. If the storage chart shows a streaming app near the top, its downloads are almost certainly why.
Message attachments, which accumulate silently
Settings → General → iPhone Storage → Messages breaks down photos, videos, GIFs and other attachments, with a Review Large Attachments option that lists them biggest first. Years of group chats add up to more than most people expect.
Settings → Apps → Messages → Keep Messages, set to one year rather than Forever, prevents it recurring. Our attachments guide covers the detail.
Photos: Recently Deleted first
Photos → Albums → Recently Deleted still holds everything you removed in the last 30 days, at full size. Emptying it is instant and often returns several gigabytes on its own.
After that, Settings → Apps → Photos → Optimise iPhone Storage keeps full-resolution originals in iCloud and smaller versions on the device. Our guide to that setting explains exactly what stays where.
Safari and app caches
Settings → Apps → Safari → Clear History and Website Data clears the browser cache. It is smaller than people expect — usually hundreds of megabytes rather than gigabytes — and it signs you out of sites, so it is worth doing but is not the big win.
Most other apps have no user-facing cache control. For those, deleting and reinstalling the app is the only way to clear it, which is why offloading is generally the better tool.
System Data, and why chasing it is usually wrong
System Data is the catch-all for caches, logs and temporary files that do not belong to any app. It inflates over time and shrinks on its own when iOS needs room, and there is no button to clear it.
It is also where most bad advice on this topic lives. Our System Data guide covers what actually reduces it and what is a waste of an afternoon.
When you are freeing space for an update
An iOS update needs roughly twice its download size free — around 15 GB for a major release — and it checks at install time, not download time. That is why the failure so often arrives after a long download.
If you cannot get there, updating through a computer needs far less room on the phone because the unpacking happens on the computer. Our computer update guide covers it, and our update storage guide covers the case specifically.
Frequently Asked Questions
What frees up the most space on an iPhone?
Offloading large apps, then clearing downloaded video from streaming apps, then emptying Photos → Recently Deleted. Those three cover most cases.
Does offloading an app lose my data?
No. Offloading removes the app but keeps its documents and data. Tapping the icon reinstalls it exactly as it was.
Why is my storage still full after deleting things?
Photos → Recently Deleted holds deletions for 30 days at full size, and the storage chart takes a while to recalculate. Empty that album and give it a few minutes.
How much free space does an iPhone need?
Leave a few gigabytes free for normal operation, and around 15 GB free if you are installing a major iOS update.