You can encrypt an external drive on a Mac with Disk Utility or Finder. Encryption protects the files stored on the drive with a password, so someone who finds or removes the drive cannot normally read its contents without that password.
The best method depends on whether the drive already contains files:
- Encrypt an existing compatible volume when you want to preserve its files.
- Erase and format the drive with encryption when it is new, empty, or you have already backed up everything on it.
Before starting, make sure you have a current backup. If you lose the encryption password or recovery information, recovering the files may not be possible.
Quick Answer
To encrypt an existing external drive without erasing it, connect the drive, open Finder, Control-click the drive in the sidebar, and choose Encrypt [drive name]. Enter and confirm a password, then let macOS finish the encryption process.
To erase and encrypt a drive, open Disk Utility, select the correct volume, click Erase, choose an encrypted format such as APFS (Encrypted) or Mac OS Extended (Journaled, Encrypted) when available, set a password, and click Erase. This permanently deletes the existing data on that volume.
Before You Encrypt an External Drive
Encryption changes how the drive is accessed. Consider these points before proceeding:
- Back up important files first. Encryption should not normally delete files when applied to an existing volume, but unexpected interruptions, drive problems, or selecting the wrong disk can cause data loss.
- Choose a password you can recover. A forgotten password can make the drive’s contents inaccessible. Store the password in a trusted password manager.
- Check how you will use the drive. An encrypted APFS drive works well for Macs, but it may not work natively with Windows computers or other devices.
- Keep the drive connected. Do not unplug it, put the Mac to sleep, or force a restart while encryption is in progress.
- Quit apps using the drive. Close documents, backup tools, media libraries, and other apps that are reading from or writing to the external disk.
If you need to use the drive with both macOS and Windows, review the format choice carefully. APFS vs exFAT: Which Format Should You Use on a Mac? explains the main compatibility differences.
Method 1: Encrypt an Existing External Drive Without Erasing It
This method is generally the most convenient option when the external drive already contains files and you want to keep them. macOS must support encryption for the volume’s current format. If the encryption option does not appear, use the erase-and-format method instead.
Encrypt the drive in Finder
- Connect the external drive to your Mac.
- Open Finder.
- In the Finder sidebar, locate the drive under Locations.
- Control-click the drive, or right-click it.
- Choose Encrypt “[drive name]”.
- Enter a password when prompted.
- Enter the password again to confirm it.
- If macOS offers a password hint, enter one that does not reveal the password to other people.
- Click Encrypt Disk or the equivalent confirmation button.
macOS begins encrypting the volume. You may continue using the Mac, but avoid disconnecting the drive until the process finishes. Large drives or drives with many files can take considerable time.
When you later connect the encrypted drive, macOS displays a password prompt. Enter the encryption password to mount the volume and access its files.
If Finder does not show an encryption option
The Encrypt command may be unavailable for some drive formats, partitions, or storage configurations. It may also be missing if you selected a physical disk instead of an individual volume.
Try these checks:
- In Finder, confirm that you selected the mounted volume under Locations.
- Open Disk Utility and inspect the drive’s format.
- Make sure the drive is writable and not locked by hardware.
- Copy the files to another location.
- Erase and reformat the volume using an encrypted format.
Erasing is not a continuation of the first method—it is a separate process that removes the existing data.
Method 2: Erase and Format the Drive With Encryption
Use this method for a new or empty drive, or when you have safely backed up its contents. It creates an encrypted volume from the beginning.
Warning: Erasing a volume permanently deletes all files on it. Confirm the selected drive and make a backup before clicking Erase.
Choose an encrypted format
The available encrypted formats depend on the drive and macOS configuration. Common choices include:
- APFS (Encrypted): Usually the best choice when the drive will be used primarily with Macs. APFS is designed for modern macOS storage.
- Mac OS Extended (Journaled, Encrypted): An older encrypted Mac format that may be useful in some legacy or compatibility situations.
Do not choose an encrypted Mac format if you need the drive to work directly with devices that do not support it. Cross-platform use may require different software or a different storage strategy.
Erase and encrypt the external drive
- Connect the external drive to your Mac.
- Quit any apps using the drive.
- Open Disk Utility. You can find it in Applications > Utilities or by searching with Spotlight.
- In the menu bar, choose View > Show All Devices if you need to see the physical disk and its volumes.
- In the sidebar, select the volume you want to erase. If you intend to erase the entire device, carefully select the physical external disk instead.
- Click Erase in the toolbar.
- Enter a recognizable name for the encrypted volume.
- Open the Format menu.
- Choose APFS (Encrypted), or another encrypted format appropriate for your intended use.
- If Disk Utility asks for a Scheme, choose GUID Partition Map for a Mac-focused drive.
- Click Erase.
- Create and confirm a strong password when prompted.
- Click Choose or the confirmation button, then wait for Disk Utility to finish.
- Click Done.
The newly encrypted volume should mount in Finder. Eject it, reconnect it, and verify that macOS asks for the password before relying on the drive for important files.
For more information about the erase process and format choices, see How to Format an External Drive on a Mac.
How to Use an Encrypted External Drive
After encryption is enabled, the drive behaves much like any other external volume when it is unlocked.
- Connect the drive to your Mac.
- Wait for the password prompt.
- Enter the encryption password.
- Use the drive normally in Finder.
- When finished, close files stored on the drive.
- Eject the volume before disconnecting it.
Encryption protects data while the volume is locked or disconnected. Once you unlock and mount it, files can be opened by anyone who can use your logged-in Mac account and access the mounted volume. Lock the Mac and eject the drive when you are finished.
If the drive does not eject, close files and apps that may be using it. How to Safely Eject an External Drive on a Mac covers safe removal steps.
What to Do if You Forget the Password
There is no general password-reset step that bypasses encryption and preserves access to the files. Depending on how the volume was created, macOS may offer a recovery option, such as a recovery key or an account-based recovery choice. If you saved one, use it exactly as instructed.
If no recovery option is available, the practical solution may be to erase the encrypted volume and restore the files from a backup. Erasing removes the encrypted data, so do not do this until you have confirmed that no recovery method or backup remains.
Troubleshooting
The password prompt does not appear
The volume may already be unlocked, or macOS may have mounted it automatically after you entered the password earlier. Eject the volume, disconnect it safely, and reconnect it to test the lock behavior.
If it still opens without a prompt, check whether you encrypted the correct volume. A physical disk can contain multiple separate volumes, and encrypting one does not automatically encrypt every other volume.
The drive is not visible in Finder
Open Disk Utility and check whether the drive appears in the sidebar.
- If it appears but is not mounted, select the volume and click Mount.
- If it appears dimmed, the volume may be unmounted, damaged, or locked.
- If the physical disk does not appear at all, check the cable, adapter, power supply, and port.
- Try connecting the drive directly instead of through a hub.
Do not erase the drive simply because it is not visible in Finder. First determine whether the Mac recognizes the physical device.
Encryption appears stuck
Encryption can take time, especially on a large or nearly full drive. Keep the Mac powered on and leave the drive connected. Avoid interrupting the process unless macOS reports an error.
If the Mac becomes unresponsive, wait before forcing a restart. Afterward, reconnect the drive and check whether it mounts. If the volume does not mount or reports errors, use Disk Utility’s First Aid feature before attempting any erase operation.
Disk Utility reports that the erase failed
Check that you selected the correct volume or physical disk and that no application is using it. Eject the drive, reconnect it, and try again.
If you selected a physical disk, make sure View > Show All Devices is enabled so you can distinguish the device from its volumes. Persistent errors may indicate a failing drive, cable, enclosure, or adapter.
I need to use the drive on Windows
An encrypted APFS or Mac OS Extended volume is intended primarily for Mac use. Windows may not read it without additional software, and that software may not support every encryption configuration.
If the drive must move between Macs and Windows PCs, decide whether native cross-platform access is more important than using macOS’s built-in encrypted formats. Back up the data before changing the format, because reformatting erases the volume.
I cannot write files to the encrypted drive
The volume may be formatted as a Mac-only file system, mounted read-only, or affected by permissions or disk errors. Check the format in Disk Utility and confirm that the volume is unlocked and writable.
If the drive was previously used with another operating system, copying the files elsewhere and reformatting the drive may be necessary. This deletes the existing contents, so verify your backup first.
Frequently Asked Questions
Does encrypting an external drive delete its files?
Encrypting an existing compatible volume through Finder is designed to preserve its files. However, you should always create a backup before starting. Erasing and choosing an encrypted format deletes the volume’s existing contents.
Is an encrypted external drive password protected?
Yes. You normally need the encryption password to unlock and mount the volume. The password protects the data on the drive, not necessarily the Mac itself or files copied to another location.
Can I encrypt a USB flash drive on a Mac?
Often, yes, if the drive uses a compatible writable volume. Flash drives can be slow or unreliable during large operations, so back up the contents first and avoid disconnecting the drive while encryption is underway.
Can I change the encryption password?
The available password-management options depend on how the volume was encrypted and which macOS tools are available. Do not erase the drive to change a password unless you have a verified backup. If you cannot find a password-change option, copy the data to another secure location and create a new encrypted volume.
Does encryption protect files while the drive is unlocked?
No. Once the volume is unlocked and mounted, its files can generally be accessed by an authorized user of the Mac. Eject the drive when it is not in use, and lock your Mac when you step away.
Should I encrypt a Time Machine drive?
Encryption can protect backups stored on an external drive, but the correct setup depends on how the drive is being used and which backup features are enabled. Do not erase an existing backup disk until you have confirmed that you have another usable backup.
Final Thoughts
The simplest way to password protect an existing compatible external volume is to use Finder’s Encrypt command. If that option is unavailable—or if the drive is new or empty—use Disk Utility to erase it and create an encrypted format. In both cases, back up your files, protect the password, and safely eject the drive whenever you finish using it.