One of the trickier aspects of buying an iPhone is deciding how much storage you'll need, and how much you can afford. The price jumps for the upper tiers are not small, but you can't upgrade the device's storage later. It's a conundrum.

If you do find yourself short of space, however, there are some solutions. They might not have SD slots but iPhones can be used with a range of external storage devices. Or you can store important and/or bulky files off-device, by signing up for a reliable cloud storage service.

This has the added benefit of creating a backup that you can still access if your phone gets bricked - although we would recommend the use of multiple backups for irreplaceable files just in case the cloud service suffers a breach or outage.

In this article we round up the best cloud storage apps and services for iPhone owners, rating them for reliability, security, ease of use and value for money.

iCloud

Best Cloud Storage Apps for iPhone: iCloud

  • 5GB: free
  • 50GB: 79p/99c a month
  • 200GB: £2.49/$2.99 a month
  • 2TB: £6.99/$9.99 a month

The most obvious choice first: Apple's own iCloud offering has the advantage of total integration throughout iOS, simplicity of use, and not having to download an app. We would also be more willing to trust Apple with our data than many other companies, because of its generally very high product standards and demonstrated commitment to privacy.

(No cloud service is perfect, of course. iCloud was subject to a high-profile leak in 2014, but this appears to have been achieved by phishing for passwords rather than breaching the service's security. And Apple responded by encouraging users to use two-step verification.)

On the downside, iCloud doesn't work terribly well with PCs, and the free allowance of 5GB (which applies no matter how many Apple devices you've got), is hardly enough to store anything. The prices are pretty good, in our view - there are plenty of costlier alternatives out there.

Sign up to iCloud

Google Drive

Best Cloud Storage Apps for iPhone: Google One

  • 15GB: free
  • 100GB: £1.59/$1.99 a month
  • 200GB: £2.49/$2.99 a month
  • 2TB: £7.99/$9.99 a month
  • 10TB: £79.99/$99.99 a month
  • 20TB: £159.99/$199.99 a month
  • 30TB: £239.99/$299.99 a month

Like Apple, Google offers a cloud storage service that is accessed via multiple apps. The service has a confusing mixture of names, as for Android users it goes under the umbrella term of Google One, while the iOS app is called Google Drive. This doesn't really become an issue if you're iOS only, but should you see Google One being mentioned on your Mac or PC then rest assured that it's basically the same service, just with a different name. There are plans to harmonise the two, but at the time of writing this has yet to be achieved.

You can also access Google's cloud storage via Docs, Sheets, Photos and so on, and sync between your phone and Mac using Backup and Sync; this versatility makes Google a great choice for your cloud storage provider. And while Drive is simple (and pleasingly easy to use), the other apps in the suite offer powerful features - Photos, for instance, is one of the best offerings of its type out there.

Google is three times as generous as Apple when it comes to your free allowance, but perhaps unexpectedly it is slightly more expensive for UK customers than iCloud at the 2TB tier. If you want huge storage capacity then Google Drive goes up to a massive 30TB, but you'll be paying corporate-level prices for the space.

Sign up to Google Drive

Microsoft OneDrive

Best Cloud Storage Apps for iPhone: OneDrive

  • 5GB: free
  • 50GB: £1.99/$1.99 a month
  • 1TB: £5.99/$6.99 a month, or £59.99/$69.99 a year*
  • 1TB per user, for up to six users: £7.99/$9.99 a month or £79.99/$99.99 a year*
    *As part of an Office365 subscription

We're back to iCloud levels of stinginess again, with only 5GB offered for free. But in other respects Microsoft is a surprisingly suitable choice of cloud provider for an iPhone owner, especially one who uses a PC.

OneDrive syncs quite happily with Macs too, mind you, and its platform agnosticism is one of its great strengths. Families with numerous different devices would be well advised to consider this option.

The app itself has a couple of interesting features to explore. One is a personal vault where documents can be locked away and only accessed via two-step authentication, with Face ID and Touch ID both supported. The other is a scanner that can covert documents, whiteboard images, business cards and photos into digital formats. You can even combine the two by directly scanning the image into your personal vault, which could be useful for having your driver's license or passport details on hand at any time.

Perhaps the most tempting of all the tiers are the 1TB offerings. These may seem a little less impressive than the 2TB tiers for similar prices on Google Drive and iCloud, but Microsoft's deals are inclusive of an Office365 subscription, meaning you get full copies of Microsoft Office (Word, Excel, Powerpoint, and Outlook) that can be used on your Mac, PC or mobile devices.

If you're a family that needs these apps for personal use or the kids' homework, then it is a hugely tempting way to keep down costs.

Sign up to OneDrive

Box

Best Cloud Storage Apps for iPhone: Box

  • 10GB, 250MB file limit (Individual): Free
  • 100GB, 5GB file limit (Personal Pro): £8/$10 a month
  • 100GB, 2GB file limit (Starter): £4/$5 a month (per user)
  • Unlimited storage, 5GB file limit (Business): £12/$15 a month (per user)

Splitting the difference between Apple and Google, Box offers a steady 10GB of free storage. This is limited to 250MB files though, so if you were hoping to store large video files then you may need to look elsewhere.

Its 100GB offering is by a distance the most expensive here (note that if you go for the Starter plan you must subscribe for at least three users, so that isn't a budget option), but once you get to the Business plan overall storage is unlimited - although there is a 5GB cap on individual files. You can read details of the pricing plans for individuals and for businesses.

The high prices make Box generally a choice for businesses, not civilians, although the relatively generous free tier may be appealing if you'd rather not go with Google.

Sign up to Box

Dropbox

Best Cloud Storage apps for iPhone: Dropbox

  • 2GB: free
  • 2TB (Plus): £7.99/$9.99 a month
  • 2TB (Professional): £16.58/$16.58 a month

We take it all back, iCloud: you no longer seem stingy. Dropbox offers the least free storage of all, at just 2GB on its Basic tier. This is hardly worth bothering with these days, especially in light of al the other options listed above. Dropbox seems to be focussed more on business customers or those using their storage for work, as the next tier is the 2TB Plus that costs £7.99/$9.99p/m or the 3TB Professional that will set you back £16.58/$16.58p/m.

The feature set is relatively limited (you get more search and sharing features if you go for the Professional subscription) and the user experience not the best. Why do so many people turn to Dropbox, then? It's good at syncing across multiple devices, although that isn't rare these days. Maybe it's just that a lot of us got used to Dropbox when decent-quality cloud services were thinner on the ground.

Sign up to Dropbox

Tresorit

Best Cloud Storage Apps for iPhone: Tresorit

  • 3GB (Basic): Free
  • 200GB (Premium): £8/$12.50p/m

Tresorit is a little different to many of the cloud storage options on this list, in that its primary focus is on security and privacy. The service offers full end-to-end encryption of files but still enables you to share them with others via secure links. These can be set to expire after a certain period, plus you can limit the amount of times it can be downloaded and by whom.

The difference here is that the encryption takes place on your device rather than in the Tresorit servers, so no one knows what's in the files except you, and more importantly no-one can decrypt them without your password. To make things even more secure you can set up two-factor authentication, and should the worst scenario occur you're able to wipe files remotely.

Tresorit is available on macOS, Windows, iOS, Android and Linux and there is a free trial of the Premium tier that gives you 14 days to see if you need the extra features and 200GB storage. Once this is over your account will revert to the Basic (free) tier with 3GB of space.

You won't really want Tresorit for storing holiday snaps and other ephemera, but for sensitive documents and data it is an excellent solution.

Sign up for Tresorit