iPhone Storage Size Calculator: 128GB, 256GB or 512GB?

What actually fills an iPhone (and why 128GB isn't 128GB)

Apple sells storage in decimal gigabytes, where 1 GB is 1,000,000,000 bytes. Your phone reports it in binary, where 1 GiB is 1,073,741,824 bytes. Same silicon, smaller number: a "128GB" iPhone formats to about 119 GB before it has done anything at all. That is not Apple being sneaky, it is just two counting systems, and Apple documents it.

Then iOS takes its cut. iOS 26 and the preinstalled apps run about 14 GB. System Data, the drawer of caches, logs, Siri assets and streamed-video buffers that nobody can quite explain, settles around 7 GB in normal use. Apple Intelligence reserves about 7 GB more for on-device models. Add it up and roughly 28 GB is spoken for before your first photo.

Ninety-one gigabytes is the real number on a 128 GB iPhone. Nine hours of 4K video, or about 36,000 HEIC photos, or one big game and a Netflix habit and rather less of both.

128GB vs 256GB: the honest breakdown

128 GB is for the cloud-first. If iCloud Photos is on with Optimise iPhone Storage, you shoot stills rather than video, and you trade the phone in every two years, 128 GB is fine and the upgrade is money burned. The catch is that you are paying Apple monthly instead, which is the trade, not a free lunch.

256 GB is the default for anyone who shoots video. One hour of 4K/30 is about 10 GB. Two school plays, a holiday and a birthday and you have eaten a third of a 128 GB phone in clips you will watch once. If you record video at all regularly, this is the tier.

512 GB and 1 TB are for ProRAW, ProRes, and five-year owners. A thousand ProRAW frames is 75 GB on its own. If you keep a phone until it dies and carry your whole library plus offline films, the headroom is the point.

One more piece of arithmetic before you decide. That $100 upgrade step is 33 months of iCloud+ 200 GB at $2.99 a month, so nearly three years of cloud for the price of one storage step. The phone storage is yours, though. It comes back at resale and it works with no signal, whereas the iCloud plan is rent you can stop paying. Neither answer is wrong. Just know which one you are choosing. The iCloud Storage Cost Calculator prices the rental side properly.

The cheaper answer: you probably don't need the upgrade

Avast looked at nearly 3 billion photos across 6 million people and found that 22% of them were junk: 16% duplicates and near-identical burst frames, 6% blurry, dark or otherwise unusable. Most people are not out of storage. They are carrying a library where a fifth of it was never worth keeping, and paying Apple $100 to keep carrying it.

Run the numbers above with the cleanup applied and watch what happens: for plenty of libraries, a clean 128 GB fits where a cluttered one did not. That is the $100 back, and the monthly iCloud bill down a tier with it.

Swipe44 is the part that gets it done. Swipe right to keep, left to delete, working through Recents, Random or a single month at a time, so a session takes ten minutes instead of a lost afternoon. Duplicates are found by perceptual hashing on the phone itself and grouped for review, including the burst frames the built-in Duplicates album walks straight past. Anything you mark waits in a pending pile you can walk back, and one system confirmation clears the batch. Then the app tells you how much space actually came back. No account, no uploads, and iCloud originals are never downloaded.

How this calculator works

Here is every constant it runs on, so you can argue with the ones you disagree with.

The arithmetic: monthly photo growth is your photo count times MB per photo, times 1.25 if WhatsApp or Messages auto-saves to your roll. Monthly video growth is minutes times MB per minute. Multiply both by the months you keep the phone, add whatever library you are bringing over, then add apps, games and offline media. A tier is recommended when it has at least 10% headroom left and does not fill before your ownership period ends.

Optimise iPhone Storage is modelled as a cap: iOS keeps lighter versions on the phone and the originals in iCloud, and the device library never runs past about 35% of usable capacity (with an 8 GB floor). Worth being blunt about, because most write-ups are not: that caps what the phone holds, not what you pay. The full-resolution originals still sit in iCloud and you still rent the space for them.

Treat the output as a model, not a measurement. Compression depends on what is in the frame, real libraries mix formats, and System Data drifts. For your actual figures, open Settings, then General, then iPhone Storage.