The short answer
On most full iPhones the space is taken by five things, in roughly this order: 4K video, Messages attachments kept forever, near-identical photo bursts, cached app data, and high-resolution capture formats like ProRAW. Apps themselves are rarely the problem. One hour of 4K 60 fps video alone can use more space than every app on the phone combined.
Open Settings → General → iPhone Storage and you get a coloured bar and a list of apps sorted by size. The list is misleading in a specific way: it shows you the *container* an app owns, not what is inside it. Photos sits at the top with 60 GB and tells you nothing about whether that is 400 irreplaceable pictures or 40 copies of the same sunset.
This is a breakdown of what is actually in those containers, with real figures, ordered by how much space each one typically claims. Every number below is one you can verify on your own device, and I have said where to look.
4K video — the single largest line item on most phones
Typical reclaim: 5–40 GB
Video is not slightly bigger than photos. It is bigger by two orders of magnitude. A 12-megapixel HEIF photo is roughly 2–3 MB. One minute of 4K 60 fps video is in the region of 225 MB in HEVC — about a hundred photos per minute of recording.
| Recording setting | Approx. per minute | Approx. per hour |
|---|---|---|
| 1080p, 30 fps | ~40 MB | ~2.4 GB |
| 1080p, 60 fps | ~60 MB | ~3.6 GB |
| 4K, 30 fps | ~112 MB | ~6.7 GB |
| 4K, 60 fps | ~225 MB | ~13.5 GB |
| ProRes 4K, 30 fps | ~1.2 GB | ~72 GB |
What to do about it
Two separate decisions, and people usually only make the first.
Going forward: if you are not cutting footage in an editor, 4K 60 is paying a large storage bill for a benefit you will never see on a phone screen. 4K 30 halves it. 1080p 60 — still perfectly good, still slow-motion-capable — cuts it by roughly three-quarters.
For what you already have: sort by size rather than hunting by hand. In Photos, open Albums → Media Types → Videos, and look for the long ones you forgot about — the 22-minute clip of a concert, the accidental in-pocket recording, the three takes of the same birthday toast. A handful of those is usually several gigabytes.
Messages attachments, kept forever by default
Typical reclaim: 2–20 GB
This is the most commonly overlooked one, and often the largest after video. By default iOS keeps every message *and every attachment* forever. Every meme, every screenshot someone sent you in 2019, every video your group chat reacted to — all still on the phone.
Check the real figure: Settings → General → iPhone Storage → Messages. iOS breaks it into Photos, Videos, GIFs and Stickers, and Other. People are routinely surprised by the Videos line.
What to do about it
- 01
Review the largest attachments first
In Settings → General → iPhone Storage → Messages, tap a category such as Videos and then Edit. You can delete the biggest items individually without touching the conversations themselves.
- 02
Decide whether you need a decade of history
Settings → Apps → Messages → Keep Messages offers 30 Days, 1 Year, or Forever. Switching to 1 Year is the single highest-yield setting change on this entire page for most people.
- 03
Turn off automatic saving
In the same Messages settings, Auto-Save Shared Photos copies images from conversations into your library — doubling them. Turning it off stops the duplication at the source.
Near-identical photos — the ones Apple's Duplicates album does not catch
Typical reclaim: 1–15 GB
Modern iPhones have a Duplicates album built in — Albums → Utilities → Duplicates — and it works well for what it targets: true copies. The same image saved twice, an import that ran twice, a picture you saved from a chat that was already in your library.
What it does not surface is the far more common case: the *eleven* photos you took of one moment, where everyone blinked in four of them, two are slightly tilted, and one is the keeper. Those are not duplicates in any technical sense — every file is genuinely different — so they stay, all of them, forever.
Fifty-five megabytes is nothing. The problem is that this pattern repeats across every birthday, every holiday, every dog photo, for years. In a library of 20,000 photos, the near-duplicate tail is routinely 20–40% of the count.
What to do about it
There is no setting for this, because the decision is genuinely subjective — only you know which of the eleven is the keeper. It is a review problem, not a detection problem, and the only honest options are to work through it manually in the Photos app or to use a tool built for fast one-at-a-time triage. I compare the main ones, including my own, in the photo cleaner roundup.
Cached app data that reports as the app's size
Typical reclaim: 1–10 GB
When iPhone Storage says Spotify is 9 GB, Spotify is not 9 GB. The app is perhaps 150 MB; the rest is downloaded music, cached artwork, and offline data. iOS reports the app and its data as one number, which is why deleting apps feels so unpredictable — sometimes it frees 80 MB, sometimes 9 GB.
The usual offenders are the ones that cache media aggressively: streaming music and video, podcasts, social feeds, and anything with offline downloads. WhatsApp deserves its own mention — it auto-downloads media you never opened and, with one setting on, stores a second copy of every received photo in your camera roll. Why WhatsApp gets so large covers the four settings behind it.
| What it is | Where it shows up | How to clear it |
|---|---|---|
| Offline downloads | Spotify, Apple Music, Netflix, podcasts | In-app: remove downloads from the app's own library screen |
| Browser cache | Safari | Settings → Apps → Safari → Clear History and Website Data |
| Social feed cache | Instagram, TikTok, X | No in-app control; requires offload or reinstall |
| Documents & Data | Most apps | Varies — many apps have no clear-cache option at all |
Offload vs delete — and why the difference matters
iOS gives you two options, and they are not interchangeable:
- Offload App removes the app binary but keeps its documents and data. Reinstalling restores your state. This frees the *least* space, because the cache is usually the bulk of it.
- Delete App removes the app and all of its data. This frees the most space and is the only reliable way to clear a cache for an app that offers no in-app control — but you lose anything stored locally and not synced.
High-resolution capture formats you may have switched on once
Typical reclaim: 2–20 GB, and growing
This one is insidious because it is a setting, not a pile of files: it does not cost you anything today, it costs you every photo you take from now on.
Apple is blunt about the headline figure. On ProRAW: *"ProRAW files are 10 to 12 times larger than HEIF or JPEG files."* In practice that is roughly 25 MB for a 12 MP ProRAW file and roughly 75 MB at 48 MP, against 2–3 MB for a standard HEIF.
| Format | Approx. size per photo | Multiplier vs HEIF |
|---|---|---|
| HEIF (default) | ~2–3 MB | 1× |
| JPEG (Most Compatible) | ~4–6 MB | ~2× |
| Live Photo | ~5–6 MB | ~2× |
| ProRAW 12 MP | ~25 MB | ~10× |
| ProRAW 48 MP | ~75 MB | ~30× |
What to do about it
Audit three settings and decide each one deliberately:
- 1Settings → Camera → Formats — if ProRAW or ProRes is on and you are not editing in Lightroom or Final Cut, turn it off. Leave High Efficiency selected rather than Most Compatible.
- 2Settings → Camera → Preserve Settings — if ProRAW is left enabled here, every camera launch starts in ProRAW. Many people turn the format on for one shoot and never notice it stayed on.
- 3Settings → Camera — Live Photos roughly doubles the cost of each still, because each one stores a short video alongside the image. Worth keeping if you use them; worth switching off if you do not.
The order to actually do this in
If you are out of space right now and want the fastest route to a usable phone:
- 01
Empty Recently Deleted
Photos → Collections → Utilities → Recently Deleted. If you have deleted anything in the last 30 days, it is still occupying space. This is free, instant, and the reason most people think deleting photos "did nothing" — covered properly in why your storage does not go down.
- 02
Delete your five longest videos
Albums → Media Types → Videos. Five clips is often 5–10 GB, and takes about a minute.
- 03
Change Keep Messages to 1 Year
One setting, frequently several gigabytes. Save anything irreplaceable out of your conversations first.
- 04
Bulk-delete the Screenshots album
Albums → Media Types → Screenshots. No judgement calls required.
- 05
Fix your capture settings
Settings → Camera. Frees nothing today; stops the problem recurring in six months.
- 06
Then, and only then, review near-duplicates
This is the slow one. Do it when you have the time and attention, not when you are trying to install an update.
Common questions
Does deleting apps free up much space?
Usually less than people expect, and unpredictably. The number next to an app in iPhone Storage includes its cached data, so deleting a 9 GB Spotify entry frees 9 GB only because of downloaded music — the app itself is a fraction of that. Video, Messages attachments and photos account for far more space on a typical full phone.
Why does iPhone Storage show a different total to the sum of the apps?
Two reasons. The coloured bar includes System Data and iOS itself, which are not listed as apps, and the figures are cached — they can lag by minutes to hours after you delete something. If the numbers look wrong, give it time or restart the phone before concluding something failed.
Will buying more iCloud storage fix a full iPhone?
Only if you also switch on Optimize iPhone Storage, and even then only for photos and videos. iCloud storage and device storage are different things — paying for iCloud does not by itself move anything off the phone. What each iCloud Photos setting actually does covers the distinction.
Is System Data the real problem?
Rarely, despite how alarming it looks. System Data is a catch-all for caches, logs and temporary files, it fluctuates on its own, and iOS clears much of it automatically under pressure. If it has ballooned to tens of gigabytes and stayed there, a backup-and-restore is the only reliable fix — but check the five categories above first, because they are almost always the actual cause.
How much free space should I leave on an iPhone?
Aim for at least 10% free, and ideally 10–15 GB. iOS needs working room for updates, camera capture and app installs, and a phone running at 99% full gets visibly slower and starts refusing to record video mid-clip.