To format an external drive on a Mac, open Disk Utility, select the correct physical drive, click Erase, choose a format and partition scheme, and confirm. Formatting erases everything on the selected drive, so copy any files you want to keep before continuing.
For most uses, choose:
- APFS for a drive used primarily with modern Macs
- Mac OS Extended (Journaled) for older Macs or certain legacy workflows
- exFAT for a drive that must work with both macOS and Windows
- GUID Partition Map as the partition scheme for a Mac startup or general-purpose drive
Quick Answer
- Connect the external drive to your Mac.
- Back up or copy any important files from it. The erase process deletes the drive’s contents.
- Open Disk Utility from Applications > Utilities.
- Choose View > Show All Devices.
- Select the physical external drive—not only a volume beneath it.
- Click Erase.
- Enter a name, choose a format, and select a scheme if shown.
- Click Erase, wait for the process to finish, and then click Done.
- Confirm that the drive appears in Finder and works as expected.
Before You Format an External Drive
Formatting, sometimes called erasing or reformatting, prepares a storage device for use with a file system. It also removes the files, folders, and volumes currently stored on the selected disk.
Before opening Disk Utility:
- Copy important files to another drive or cloud storage.
- Close files and apps using the external drive.
- Make sure you have selected the correct disk. Erasing the wrong disk can permanently delete your Mac’s data.
- If the drive contains a Time Machine backup, do not erase it unless you intend to remove that backup.
- If the drive is encrypted, make sure you know the password for any files you plan to copy before erasing it.
If the drive contains unsaved work or files currently open, close those apps first. The erase process cannot preserve unsaved changes.
Choose the Right Format
The format determines how macOS organizes files on the drive and which operating systems can use it.
APFS
APFS is Apple’s modern file system. Choose it when:
- The drive will be used mainly with Macs.
- You want a format designed for current macOS storage.
- The drive is an SSD or another flash-based storage device.
- You plan to use the drive for Mac applications, file storage, or a bootable macOS installation where supported.
APFS is generally not the best choice for a drive that must also be used regularly with Windows. Windows does not normally provide built-in full read-and-write support for APFS.
Disk Utility may show several APFS options, including encrypted and case-sensitive variants. For a standard external drive, APFS is usually the simplest choice. Choose APFS (Encrypted) only if you want the drive protected by a password and understand that losing the password may prevent access to the data.
Mac OS Extended (Journaled)
Mac OS Extended (Journaled) is an older Mac file system. It can be appropriate when:
- The drive must work with older Macs.
- You are following instructions for older Mac software or hardware.
- The drive is a traditional hard disk and will be used only with Macs.
- A specific application or workflow requires it.
It is not a convenient format for sharing files with Windows computers. Modern Macs can read and write it, but APFS is usually the more appropriate default for many Mac-only uses.
exFAT
Choose exFAT when the drive must be used with both macOS and Windows. It is useful for:
- Sharing large files between Macs and PCs
- USB flash drives
- External hard drives used on different computers
- Media that needs broad compatibility
Unlike FAT32, exFAT supports individual files larger than 4 GB. However, exFAT does not provide the same Mac-specific features as APFS, such as native support for some Mac permissions and storage features.
MS-DOS (FAT)
MS-DOS (FAT), commonly associated with FAT32, is mainly useful for older devices and compatibility situations. It has a 4 GB maximum size for an individual file, so it is usually a poor choice for modern video files, disk images, and other large files.
Choose the Correct Partition Scheme
The partition scheme describes how the drive’s partitions are organized. Disk Utility may call this the Scheme.
GUID Partition Map
Choose GUID Partition Map for most modern Mac uses, including:
- A drive used with current Macs
- A Mac startup or installation drive
- A general-purpose external drive
- APFS or Mac OS Extended storage
GUID Partition Map is usually the right default when Disk Utility offers a scheme menu.
Master Boot Record
Master Boot Record, or MBR, is an older partition scheme commonly used for compatibility with older computers and devices. It may be appropriate for a drive that must work with a particular legacy device, but it is not the normal choice for a modern Mac-only drive.
Some devices require MBR specifically. Check the device’s documentation before choosing it.
Apple Partition Map
Apple Partition Map is an older scheme associated with older PowerPC-era Macs and legacy equipment. Most everyday users should not choose it unless an older system specifically requires it.
Format an External Drive With Disk Utility
Disk Utility is the built-in macOS app for managing storage devices. It can erase, partition, repair, mount, and inspect many internal and external drives.
1. Connect the drive
Connect the external drive directly to your Mac if possible. If you are using a USB hub, dock, adapter, or cable that supports multiple connection standards, make sure the drive receives enough power and is securely connected.
If the drive does not appear, wait briefly and check Finder. You may also need to use a different cable, port, adapter, or power source.
2. Open Disk Utility
Open Finder, select Applications in the sidebar, open the Utilities folder, and then open Disk Utility.
You can also press Command-Space to open Spotlight, type Disk Utility, and press Return.
3. Show all devices
In the Disk Utility menu bar, choose View > Show All Devices.
This view displays the physical drive at the top of a hierarchy, with containers and volumes listed beneath it. For example, an external SSD may appear as a physical device with an APFS container and one or more volumes underneath.
Showing all devices helps you select the disk itself and choose a partition scheme when necessary.
4. Identify the correct physical drive
In the left sidebar, locate the external drive. Check:
- The drive’s manufacturer or model
- Its approximate capacity
- Whether it is connected through USB, Thunderbolt, or another interface
- The volumes listed beneath it
Select the top-level physical drive, not your Mac’s internal storage and not a volume containing files you want to keep.
Warning: Erasing the wrong device can delete your Mac’s operating system, personal files, or backups. If you are uncertain, stop and verify the drive’s name and capacity before continuing.
5. Click Erase
With the external physical drive selected, click Erase in the Disk Utility toolbar.
A dialog box will appear with fields for the drive name, format, and possibly the scheme.
6. Enter a name
Type a name in the Name field. Use a short, descriptive name such as Work Drive, Mac Backup, or Shared Files.
The name identifies the drive in Finder after it is mounted. You can rename the drive later without erasing it.
7. Select the format
Choose the format that matches your needs:
- APFS for Mac-only use on modern systems
- Mac OS Extended (Journaled) for older Mac compatibility or a specific legacy requirement
- exFAT for sharing files between macOS and Windows
- MS-DOS (FAT) only for older devices or situations that require FAT32
If you choose an encrypted format, you will be asked to create a password. Store that password securely. Without it, you may not be able to access the drive’s contents.
8. Select the scheme
If Disk Utility displays a Scheme menu, choose GUID Partition Map for most modern Mac uses.
If you selected a volume rather than the physical disk, Disk Utility may not show the scheme menu. Return to the sidebar and select the top-level physical drive.
9. Confirm the erase
Review the drive name, format, and scheme. When you are ready, click Erase.
This step permanently removes the existing data from the selected drive. Do not disconnect the drive, close the Mac, or interrupt the process while Disk Utility is working.
When Disk Utility reports that the operation is complete, click Done.
10. Check the formatted drive
The drive should mount in Finder. Open a Finder window and look under Locations in the sidebar.
Test the drive by copying a small file to it, opening that file, and deleting it afterward if you do not need it. If you formatted the drive as exFAT for cross-platform use, eject it properly before connecting it to a Windows PC.
Erase a Volume Instead of the Entire Physical Drive
Sometimes you only need to remove and recreate a volume, not change the disk’s partition scheme. In Disk Utility, select the volume beneath the physical drive and click Erase.
This can be useful when:
- You want to remove the files from one volume.
- You want to keep other volumes on the same physical drive.
- The partition scheme is already correct.
However, erasing a volume does not necessarily remove every partition or volume on the physical device. If you want to completely reorganize the drive, select the physical disk and use Erase with View > Show All Devices enabled.
Be careful: selecting the physical disk can remove all volumes beneath it.
Partition an External Drive
Partitioning divides one physical drive into separate sections. Each partition can have its own volume and, in some cases, its own format.
To partition a drive:
- Open Disk Utility.
- Choose View > Show All Devices.
- Select the physical external drive.
- Click Partition in the toolbar.
- Use the controls in the partition window to add or resize partitions.
- Assign each partition a name and format.
- Review the layout carefully.
- Click Apply and confirm the changes.
Warning: Changing partition sizes or deleting partitions can erase data, especially when removing or resizing existing partitions. Back up the drive first and read Disk Utility’s confirmation message before applying changes.
For many users, a single volume is simpler and less likely to cause confusion. Use multiple partitions only when you have a specific reason, such as separating Mac-only storage from a cross-platform exFAT volume.
Safely Eject the Drive
Before disconnecting the drive:
- Close files stored on the external drive.
- In Finder, click the eject icon next to the drive in the sidebar, or select the drive and choose File > Eject.
- Wait until the drive disappears from Finder.
- Disconnect the cable.
Removing a drive while files are being written can corrupt the file system or cause data loss.
Troubleshooting Disk Utility Erase Errors
The drive does not appear
Try the following:
- Disconnect and reconnect the drive.
- Use another USB, Thunderbolt, or compatible port.
- Replace the cable or adapter.
- Connect the drive directly instead of through a hub.
- Check whether the drive requires a separate power adapter.
- In Disk Utility, choose View > Show All Devices.
- Open Apple menu > System Settings, choose General, select About, and check System Report for the connected hardware.
If the drive does not appear anywhere, the issue may involve the cable, adapter, enclosure, power supply, or drive hardware.
“Erase process has failed”
This message can have several causes, including:
- The drive is being used by an open app.
- A volume is mounted or locked.
- The disk has file-system errors.
- The drive is failing.
- The selected operation is incompatible with the current partition layout.
Close apps that may be using the drive, eject it, reconnect it, and try again. If the drive contains important data, avoid repeated erase attempts until you have recovered or backed up the files.
You can also select the volume in Disk Utility and click Unmount, then select the physical drive and try Erase again. Unmounting makes the volume unavailable to apps temporarily; it does not erase data by itself.
The Erase button is unavailable
Make sure you selected a writable external drive and not a read-only volume or disk image. Also check that the physical drive is selected when you need to change the partition scheme.
A damaged cable, failing drive, or hardware write-protection setting can also prevent erasing.
Disk Utility says the device is busy
Close Finder windows and apps that may be reading or writing to the drive. Eject the drive, reconnect it, and retry.
If the drive is used for backups, syncing, media playback, virtualization, or another background task, stop that task before erasing.
The drive is read-only
A physical write-protection switch, adapter, permissions issue, or failing device may make a drive read-only. Check the drive and adapter for a lock switch. If the drive uses removable media, such as an SD card, verify that its lock tab is in the unlocked position.
If there is no physical lock, test another cable, port, or Mac. A drive that remains read-only may be failing.
The drive works on a Mac but not Windows
If Windows must read and write the drive, erase it as exFAT with a compatible partition scheme. A drive formatted as APFS or Mac OS Extended may not provide normal built-in Windows write support.
Formatting as exFAT erases the drive, so back up its contents first.
The drive was formatted but does not appear in Finder
Open Disk Utility and check whether the volume is mounted. If it is dimmed, select it and click Mount.
Also check Finder settings. In Finder, choose Finder > Settings, select General or Sidebar, and make sure external disks are configured to appear where you want them.
Frequently Asked Questions
Does formatting an external drive erase everything?
Yes. Using Erase in Disk Utility removes the existing data from the selected volume or physical disk. Back up anything important before confirming the operation.
What format should I use for a Mac external drive?
Use APFS for most modern Mac-only uses. Use Mac OS Extended (Journaled) when older Mac compatibility or a specific legacy application requires it.
What format works with both Mac and Windows?
Use exFAT for a drive that needs to support reading and writing on both macOS and Windows. Avoid FAT32 when you need to store files larger than 4 GB.
Should I choose APFS or exFAT for a USB drive?
Choose APFS if the USB drive will stay with Macs. Choose exFAT if you will move it between Macs and Windows PCs.
What partition scheme should I choose on a Mac?
Choose GUID Partition Map for most modern Macs and general-purpose external drives. Use another scheme only when a specific older computer or device requires it.
Can I format an external drive without Disk Utility?
Disk Utility is the safest graphical method for most Mac users. Terminal also includes disk-management commands, but a wrong command can erase the wrong device. Unless you are comfortable identifying disk identifiers and working in Terminal, Disk Utility is the better choice.
Can I change the format without deleting files?
Usually, changing a drive’s file system requires erasing and reformatting it. Back up the contents, erase the drive with the new format, and copy the files back.
Why does Disk Utility show more than one item for my drive?
Disk Utility can show the physical device, containers, partitions, and volumes. The physical device is the hardware; a volume is the usable storage area mounted in Finder. Choose the physical device when you need to erase the entire drive or change its partition scheme.
Final Thoughts
Disk Utility provides a straightforward way to format an external drive on a Mac, but the choice of device, format, and partition scheme matters. Back up your files first, select the correct physical drive, use APFS for Mac-only storage or exFAT for Mac-and-Windows compatibility, and safely eject the drive when you finish.