Formatting a USB drive erases it and creates a fresh file system. The format you choose determines which computers can read/write it and whether large files are supported.
This guide applies to USB flash drives and external drives formatted with Disk Utility on macOS.
Does This Affect You?
Use these steps when preparing a USB drive for Mac backups, Mac-only storage, Windows/Mac file transfer, or older devices. Copy anything important off the drive first.
Format with Disk Utility
- Connect the USB drive.
- Open Disk Utility.
- Select the top-level physical drive in the sidebar if you want to fully reformat it, not only a volume beneath it.
- Click Erase.
- Enter a name.
- Choose the format and scheme. Use GUID Partition Map for modern Mac use, or Master Boot Record when older Windows/device compatibility requires it.
- Click Erase, then Done.
Choose the Right Format
- APFS: Best for Mac-only drives used with modern macOS versions.
- Mac OS Extended (Journaled): Good for older Mac compatibility and some older Time Machine workflows.
- exFAT: Best for moving files between Mac and Windows, with support for large files.
- MS-DOS (FAT32): Use only for older cameras, stereos, TVs, or devices that require it. It has a 4 GB single-file limit.
More Formatting Notes
Terminal diskutil Is Powerful
Advanced users can run commands such as diskutil list and diskutil eraseDisk ExFAT USBDRIVE /dev/disk4. Double-check the disk identifier because the wrong one erases the wrong drive.
If Erase Fails
Quit apps using the drive, close Finder windows showing it, select the top-level drive instead of a volume, and try again after restarting the Mac.
Partition Instead of Erase
Use Disk Utility’s Partition button if you want multiple volumes on one physical drive, possibly with different formats.
Sources
- Apple Support: Erase and reformat a storage device in Disk Utility on Mac
- Apple Support: Disk Utility file systems on Mac
- Microsoft Support: Format a USB flash drive for Windows and Mac