Move Files to an External Drive to Free Up Your Mac

A 1 TB external SSD costs less than most software subscriptions, and moving your biggest folders onto one is the fastest way to reclaim serious space on a Mac. The move itself is easy — the step people skip is verifying the copy before deleting the originals. Here's the whole process, done safely.

Copy the files to the drive first

1. Connect the drive and wait for it to appear in the Finder sidebar under Locations. If it doesn't show up, enable it in Finder → Settings → Sidebar → External disks.
2. Open a second Finder window with Cmd+N and click the drive, so you can see source and destination side by side.
3. Drag the folders you want to offload onto the drive. Dragging between two different disks always copies — you'll see a green + badge on the cursor — so your originals stay where they are.
4. Let the transfer finish completely before doing anything else. Don't unplug the drive or let the Mac go to sleep mid-copy.

Good candidates: finished video projects, old photo exports, disk images, installers, and archives you open once a year. Anything you use weekly should stay on the internal drive — external storage is slower and won't always be plugged in.

Verify the copy before you delete anything

1. Select the original folder and press Cmd+I to open Get Info. Note the size and the number of items.
2. Do the same for the copy on the external drive. The item counts should match exactly; sizes can differ by a few kilobytes because of invisible .DS_Store files.
3. Spot-check a few files — play a video, open a document — to confirm the copy is real and readable, not just present.

Prefer the Terminal? These commands only read sizes; they change nothing:

# both should report (almost) the same size
du -sh ~/Movies/Old\ Projects
du -sh /Volumes/YourDrive/Old\ Projects

Only when the numbers match should you move the original to the Trash — and remember the space isn't actually freed until you empty the Trash.

Or move in one step with Cmd+drag

Hold Cmd while dragging and Finder moves instead of copies: the folder lands on the external drive and disappears from the internal one in a single trip. It's convenient for files you could afford to lose. For irreplaceable data, copy–verify–delete is the discipline worth keeping, because a move that fails halfway is messier to untangle than a copy that fails halfway.

Either way, eject the drive before unplugging it — click the ⏏ button next to its name in the Finder sidebar. Yanking the cable mid-write is how verified copies get corrupted after the fact.

What not to offload

• Apps. Many apps misbehave or demand reactivation when run from an external volume. If an app is just taking up space, uninstall it instead.
• Anything in ~/Library. Settings, caches, and databases need to stay on the boot drive where apps expect to find them.
• Active projects. Working files on an external drive mean everything stops the day you leave it at home.
• Your Photos library. It can live externally, but it has its own move procedure — don't just drag it over while Photos is running.

One last caveat: a file that exists only on one external drive has no backup. Open System Settings → General → Time Machine → Options and make sure the drive isn't in the exclusion list if you want Time Machine to protect it too.

Format the drive properly first

A brand-new drive often ships formatted for Windows. For Mac-only use, APFS is the right choice; pick exFAT if the drive also needs to plug into a PC. Our guide to formatting an external drive on Mac covers it in five minutes.