Encrypt an external drive on a Mac in two clicks, and the one thing you must not lose
A lost USB drive or backup disk is readable by anyone unless it is encrypted. How to encrypt one from Finder or Disk Utility, and what happens without the password.
A backup drive holds a copy of everything on your Mac. If it is lost or stolen unencrypted, anyone can read it. Encrypting it takes a couple of clicks and costs no extra space.
Option 1: from Finder, keeping the files
If the drive is formatted as APFS or Mac OS Extended, Control-click it in Finder and choose Encrypt. Set a password and a hint. The drive stays usable while encryption finishes in the background, which can take hours for a large drive.
Option 2: when erasing
In Disk Utility, choose Erase and pick APFS (Encrypted) as the format. This erases the drive, so copy anything you need off it first.
Time Machine drives
When adding a backup disk in System Settings, General, Time Machine, tick Encrypt backup. For an existing backup drive, remove it and add it again with the option on.
Check it worked
diskutil apfs list | grep -E "Name|FileVault|Encrypted"| Format | Can encrypt with macOS? |
|---|---|
| APFS | Yes |
| Mac OS Extended | Yes, converting where needed |
| ExFAT or FAT32 | No, it has to be reformatted |
Encrypted drives only work on Macs. For a drive shared with Windows, see formatting for Mac and Windows. For wiping a drive before giving it away, see wiping an external drive.
Common questions
How do I encrypt an external drive on a Mac?
Control-click it in Finder and choose Encrypt, if it is APFS or Mac OS Extended. Or erase it in Disk Utility as APFS (Encrypted).
Does encrypting a drive use more space?
No. Files take the same space encrypted as they did before.
What happens if I forget the password to an encrypted drive?
The data cannot be recovered. Save the password in a password manager or your Keychain before relying on the drive.