Formatting a USB stick or external drive on a Mac or MacBook

You format a USB stick or external drive on a Mac with Disk Utility. The key choice is the format: it decides whether the stick only works on a Mac, also on Windows, or is suitable for Time Machine. This article explains step by step how to format, which format to choose and what to do when the stick does not appear.

Blue Apple repairs MacBooks in Amsterdam. If a USB stick appears on none of the ports, your MacBook's port may also be the cause; more about that at the end.

Note: formatting erases everything

Everything on the stick or drive is lost. Copy what you want to keep first. In Disk Utility also make sure you select the right drive: your internal drive is usually called "Macintosh HD", and you do not want to erase that.

Step by step

1. Connect the USB stick or drive.
2. Open Disk Utility (via Spotlight, or Applications, Utilities).
3. In the View menu choose Show All Devices. That way you see the stick itself, not only the volume on it.
4. Select the stick in the sidebar (the top level, with the maker's name).
5. Click Erase at the top.
6. Give it a name, choose the format (see below) and as scheme GUID Partition Map.
7. Click Erase and wait until it is done.

Which format to choose?

• APFS: the Mac's modern format. Choose it for an SSD or stick used only on Macs with macOS High Sierra or newer.
• Mac OS Extended (Journaled): for older Macs, or for a spinning hard drive.
• ExFAT: works on both Mac and Windows and handles large files. The best choice for a stick you share between computers.
• MS-DOS (FAT): works almost everywhere, including old devices, TVs and car radios, but files may not exceed 4 GB.

For Time Machine backups the Mac chooses the right format itself when you set up the drive in Time Machine.

Erase is greyed out or fails

• You selected the volume instead of the stick: choose the top level (see steps 3 and 4).
• "Couldn't unmount": close programs that have files from the stick open, and try again.
• The stick is write-protected: some sticks and SD cards have a small switch. Flip it.
• It keeps failing: the stick may be faulty. Try another stick to rule that out.

The stick does not appear at all

1. Try another port and, with an adapter or hub, another adapter.
2. Look in Disk Utility with Show All Devices. If it is there but not in the Finder, it is probably not formatted for the Mac: format it.
3. Check in Finder settings whether external drives are shown on the desktop and in the sidebar.
4. Try the stick in another computer.

If the stick works on another computer but on none of your MacBook's ports, the ports may be the problem. Also read dock, hub or adapter for your MacBook.

Getting files back from a stick you erased by accident

Stop using the stick and write nothing new to it. Special software can sometimes still recover something, but it is not certain. If important files are involved, have it looked at first.

What we do at Blue Apple in Amsterdam

We test whether your MacBook's USB-C ports still make good contact and pass data, and replace a damaged port. For data that is gone, we check what can still be saved. More on our pages about MacBook port repair and MacBook data recovery.

Frequently asked questions

Which format works on Mac and Windows?

ExFAT. For very old devices MS-DOS (FAT), with a maximum of 4 GB per file.

Can I format a stick without Disk Utility?

Yes, with Terminal, but Disk Utility is simpler and safer.

How do I make a bootable USB stick?

With a macOS installer and a command in Terminal. See installing an older macOS.