It’s all too easy to fill your iPhone’s storage to the brim with apps, photos, and video, but just because you can doesn’t mean you should. How full is too full? We put our iOS devices through the paces to get to the bottom of things.

RELATED: How Much Free Space Should You Leave on Your Windows PC?

Recently, we tackled the topic of how much free space your should leave on your Windows PC, but these days storage constraints on mobile devices are the pinch people feel more acutely. When you search for information about free space and iOS, nearly every search result you come across is focused on how to get more free space on your iOS devices. Little to nothing is written about how much free space you should aim for, however.

That’s due largely lack of information. First, and most importantly, there’s no real official word from Apple regarding what fixed amount or percentage of your storage you should keep free for optimum use. Other than posting free space requirements for over-the-air iOS updates (e.g. in order to OTA update to iOS 11 you’ll need X amount of free space) they don’t talk much about the matter. Second, iOS is very efficient at caching things (and then wiping those caches when needed), so sometimes what looks like a lack of space is really a more efficient use of space by iOS.

Last year, for example, there was a ridiculous tip repeated all over the internet about how you could free up space on your iPhone by going to the iTunes movie rental section, starting to rent a big film, and then cancelling the process before actually paying for the rental. The trick appeared to free up space on your iPhone but in reality all it was doing was prompting iOS to dump some cache files to make room for the big incoming movie file. Ironically, in doing so, it may have dumped files out of the cache that were actually speeding up your phone. For those readers old enough to remember the “RAM Cleaners” of yesteryear, we’re sure you’re feeling a familiar vibe.

So, there’s no official word on how much free space is ideal. But, as anyone who’s ever filled up their iPhone to the bursting point can attest, very full storage has a clear impact on performance. What’s a person to do? Well, you could test this by systematically loading and unloading your iPhone with non-cache files that iOS won’t touch during cache purges, then use your phone over several days with varying degrees of storage bloat, and from there determine where the relatively optimal amount of free space is.

Or—and we think this is a far more efficient use of your time—you could read the results we came up with when we did that very thing.

How We Tested the Free Space Problem

We rounded up a handful of iOS devices. We left each device, all running iOS 10, in the same state it was in for daily use. We removed no apps, cleared no caches, and didn’t wipe the devices or place them under any sort of sterile test conditions.

Instead, we simply and incrementally filled the storage of the devices with files that iOS wouldn’t delete automatically (photos, videos, documents, and so on), half a gigabyte at a time. Then we used the devices under normal conditions doing normal every day things—taking photos, browsing the web, sending messages, and so on—and took notes on problems that arose.

What Our Tests Showed Us

One of the first things we noticed was that absolute free space was more important than what percentage of the total storage was free. In relation to the absolute free space, there were two distinct transitions in our testing.

The first transition came when, regardless of total storage capacity, our free space dipped below 2 GB. At this point, app loading became more sluggish, switching between tabs in mobile browsers took a hair longer, and so on. It wasn’t the end of the world, but it was enough sluggishness that if we weren’t actively conducting the test we might have gotten the “maybe it’s time for an upgrade” itch. The device was still usable, just frustrating.

That sluggishness only increased as the amount of free storage continued to shrink.

The second major transition came when we hit about 1 GB of free space remaining. Once we got below the gigabyte mark, the sluggishness became more marked. And as we moved closer to 500MB of free storage on the device, the performance level of the devices plummeted. We started to see app freezes and even total device freezes. In fact, the only total device freezes we’ve experienced with modern iOS devices occurred during the tests we conducted for this article—every tested device had at least one total lockup after free storage was below 500MB.

While it’s certainly possible you can use your phone with the storage space so packed you have to delete old photos to take new photos, it’s not something we can recommend. Our formal recommendation is that you keep at least a couple gigabytes of storage free for optimal performance, as well as ensuring you have adequate room to snap a few more photos, cache a Netflix movie or Plex video before your flight, or (more importantly) successfully install over-the-air iOS updates to ensure your device is always secure.

If you’re already in a bit of a storage mess, definitely check out our guide to freeing up storage and your iPhone and iPad and, if you’re like most people and your primary storage sink is photos, definitely check out our guide to free unlimited photo storage through Google Photos.

RELATED: What To Do When Your iPhone or iPad Runs Out of Space


Profile Photo for Jason Fitzpatrick Jason Fitzpatrick
Jason Fitzpatrick is the Senior Smart Home Editor at How-To Geek. He has over a decade of experience in publishing and has authored thousands of articles at How-To Geek, Review Geek, LifeSavvy, and Lifehacker. Jason served as Lifehacker's Weekend Editor before he joined How-To Geek.
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