There are all kinds of reasons why you might want to format a drive. Perhaps you are selling you Mac and you want to completely erase it so that nobody can access your date. Or perhaps you are setting up an external drive for backups. Maybe you want to copy something onto a drive to share with a PC or another Mac. Or it might be that you bought a drive to use with your Mac only to discovered it is pre-formatted for Windows.
Fortunately Disk Utility, built right into MacOS, can help. And it's easy to use too.
Before we begin there are a few things you need to know, including the most important decision of all, which format to use.
We also have a tutorial on using Disk Utility on a Mac here. Other reasons you might want to use Disk Utility include making a bootable macOS install drive (covered here) and if you are doing a clean install of macOS.
Which file format should I use?
There are a few file formats that you can use but the one that's right for your circumstances depends very much on what you are going to be using the drive for. We'll describe them below, and you'll be able to choose the one that suits you.
APFS (Apple File System) - This is the new file system that Apple bought to Macs with High Sierra and it will be the default if you are using that version of macOS. There are a number of things that are good about it - such as it being more efficient and more reliable. You can choose an encrypted version and a case-sensitive version. But it won't be readable or usable by a Mac that isn't running High Sierra, and Windows or Linux machines won't be able to read or write either. And it currently only works on SSDs or Flash storage. Read some of the good stuff about APFS here. For now we'd advise against formatting in APFS because it won't be readable by Macs that aren't running High Sierra, but this may not matter to you.
MacOS Extended (Journaled) (also known as HFS+) - APFS replaced MacOS Extended as the default file system on the Mac when Apple launched High Sierra in 2017. If your Mac isn't updated to High Sierra it will offer MacOS Extended as the default. There's also the option of MacOS Extended (Journaled, Encrypted) which is a good choice if you are likely to be carrying your laptop or external drive around and don't want anyone to access the contents of the drive should you accidentally lose it. You can encrypt your drive and require a password to access it. There's also an option of MacOS Extended (Case-sensitive, Journaled, Encrypted) if you are likely to have file names that require capital letters. Windows can read HFS+ drives but can't write to them.
MS-DOS FAT (aka FAT32) - In FAT32's favour, it can be read and written by Mac, Linux Windows - so you might want to use this if you regularly share drives with PC-owning friends or colleagues and want them to be able to access the files you place on the drive. However, it’s an older file system and files are limited to 4GB or smaller - so it's not much use if you are copying movie files for example. FAT32 offers no security and it's more susceptible to disk errors.
ExFAT - this is similar to FAT32 above. Both Windows and Mac can read drives formatted with this. The main difference is it can store files over 4GB.
NTFS - This is Windows' default file system. MacOS can only read NTFS, it can’t write to it. Although there are third party tools that could allow you to do so.
How to format an external drive for Mac
Here's how to format a drive if you are planning to use it with a Mac.
- Launch Disk Utility. Either head to Applications > Utilities, or tap Command + Space and start typing Disk Utility.
- Once Disk Utility is open you'll see the list of available drives on the left. Choose the drive you'd like to format. NOTE that formatting your drive will erase the contents, so make sure you back it up first!
- Click on the Erase option from the four options available in the main window.
- Disk Utility will automatically choose the format for you. This may be APFS, or it may be Mac OS Extended (Journaled) depending on how the drive is currently formatted and whether you using macOS High Sierra or an older version of the OS. If you'd like to use something else click on the Formatting options to reveal the drop-down window. Choose your format you require depending on how you intend to use the formatted drive (see above for more information about the format types).
- The next step is to give the drive a name. This can be anything you like, but choose something obvious that will give you a hint as to what's on there.
- Next, click the Security Options button. This will bring up another window that enables you to choose how you'd like the drive to be formatted, with a slider ranging from Fastest to Most Secure. This is an important step if you want to make sure that any files currently on the drive are safely erased.
- Fastest will erase the drive by removing the header information, but will leave the underlying files intact, although they will be hidden. This means you or someone else could resurrect the files easily using data-recovery software, which isn't necessarily a good idea. Move the slider to the second option where it says "This option writes a single pass of zeros over the entire disk." This will overwrite the entire drive once.
- For higher security, continue moving to the slider to the right. The next step will give you the option to overwrite the drive three times. Moving it the entire way to Most Secure will overwrite the drive seven times - but you'll have to wait quite a while (depending on the size of the drive) before it will be available for you to use again.
- Click on Erase and wait while the contents is erased and the drive is made ready. A progress bar will show how the formatting of your drive is going and how long, roughly, it will take to complete.
- Now copy your files onto the newly formatted drive.
How to format an drive to use with a Mac & PC
If you want to format a drive so that you can copy files between a Mac and a PC you'll want to follow the tutorial above, but choose ExFAT from the list of format options.
How to format a drive for use with Time Machine
We have a tutorial on creating a Time Machine drive here, but perhaps the big question in the context of this particular tutorial is which format to use.
Time Machine still uses HFS+ (that's Mac OS Extended). If you have the option to format the drive you will be using for Time Machine using APFS don't. Time Machine can't currently use APFS.