If you’ve just bought yourself a shiny new external drive and can’t get it to work on your Mac, it’s possible that the drive isn’t compatible with macOS. But unlike other electronics on the market, it’s possible to reformat an external drive to work with the operating system(s) of your choice. It’s easy to do on a Mac using Apple’s built-in Disk Utility, and here’s where we show you how. 

Which file format should I choose?

When it comes to reformatting an external hard drive, the biggest decision you’ll have to make is with regards to file format. You see, there’s not one but several different file formats for you to choose from, offering various levels of compatibility between different operating systems. The file format you select largely depends on what you’ll be doing with the external drive, and which operating systems you use on a daily basis.


APFS is Apple’s choice of file format for Macs running macOS High Sierra or later. Introduced as a replacement to Mac OS Extended, the new file format offers improved efficiency and reliability, although it comes at a cost: APFS isn’t compatible with pre-High Sierra Macs, and it won’t work with Windows or Linux machines either. 

With a focus on speed and reliability, it should come as no surprise that APFS is exclusive to SSDs and flash storage devices - if you’ve got a standard external hard drive, you’ll have to opt for another option. 

Mac OS Extended

If you’re running macOS Sierra or an earlier version of macOS/Mac OS X, Mac OS Extended is the default file format. It’ll play nicely with your Mac, but like the above APFS, Mac OS Extended isn’t compatible with Windows or Linux PCs. 

You can also opt for Mac OS Extended (Encrypted) to password-protect the data on the drive - a great security feature for those dealing with sensitive data and/or travelling with an external drive. 


FAT32 is the go-to for some, offering cross-platform compatibility between Mac, PC and Linux, ideal for those that hop across different platforms on a day-to-day basis. However, the ageing file system has a big flaw: it’s limited to a maximum of 4GB, and it’s prone to disk errors too. 


ExFAT is an upgraded version of FAT32. Like its older sibling, ExFAT is compatible with Mac, PC and Linux, but doesn’t have the same 4GB file limit. While it’s not as efficient as Apple’s APFS, the universal support makes this the go-to for most external hard drive users. 


NTFS is the default file format for Windows PCs, and much like Apple’s APFS and Mac OS Extended, it’s only compatible with Windows machines. That being said, there’s no way to reformat to NTFS on a Mac (and why would you?) without splashing out on third-party software.

To make it clear, we recommend you stay away from NTFS if you’re looking to use your external hard drive on a Mac. 

How to reformat an external drive on Mac

Thankfully, reformatting an external drive on a Mac is a relatively straightforward process - Apple even ships Macs with a built-in utility to do so. It’s worth noting that reformatting a drive will erase everything stored on the drive, so make sure you transfer important files before you follow the below steps. 

  1. Connect your external drive to your Mac.
  2. Open Disk Utility. You can search for the app by accessing Spotlight (Command + Space) or by going to Finder > Applications > Utilities.
  3. Select the external drive under the External Drive subheading on the left-hand side. If you’re using more than one drive, be sure that it’s the one you want to reformat as the process is largely irreversible. 
  4. When you’re ready, hit the Erase button. 
  5. Enter the name of the drive and select the format of your choice in the Format dropdown menu. 
  6. Click Erase to reformat your drive - this shouldn’t take more than a few minutes, but it could vary depending on storage size and the type of drive you’re using. You’ll also be asked if you’d like to run First Aid on the drive before erasing - this is more for those with corrupted drives, so feel free to skip if you want.

You’re now ready to use your external drive on your Mac (along with Windows and Linux if you went for ExFAT!). For more on getting the most out of your Mac and accessories, take a look at how to use an iPad as a second screen on Mac, and how to use a PS4 or Xbox One controller on a Mac too.