What Are Scratch Disks in Photoshop and How to Clear Them on Mac

If Photoshop has ever refused to open a file or thrown the message "Could not complete your request because the scratch disks are full," you have hit one of the most frustrating storage walls on a Mac. This guide explains exactly what scratch disks are, where the files live, how to free up space while Photoshop is running, and how to clean up the orphaned temp files that Photoshop leaves behind after a crash.

What Is a Scratch Disk?

Photoshop is a memory-hungry application. When it runs out of RAM while working on large files, it spills data onto your hard drive in a temporary workspace called a scratch disk. Think of it as overflow memory written to storage. Photoshop uses it to hold undo history states, clipboard data, composite layers, and anything else that doesn't fit in physical RAM.

By default, the scratch disk is your startup volume. On a modern Mac that usually means your internal SSD. If you have a second internal drive or a fast external volume, you can assign it instead, which is worth doing if your main drive is getting tight.

Scratch Disk vs. Photoshop Cache

The terms get mixed up often, so it helps to separate them:

• Scratch disk: A temporary workspace file that Photoshop writes and reads in real time during a session. It is normally deleted when you quit Photoshop cleanly.
• Photoshop cache: Prerendered image thumbnails stored under ~/Library/Caches/com.adobe.Photoshop. These persist between sessions to speed up reopening documents.

The "scratch disks are full" error almost always refers to the first category. The disk simply does not have enough free space for Photoshop to write its working data.

Why Scratch Disks Fill Up

A few common reasons your scratch disk fills up faster than expected:

• You are editing very large files (high-resolution composites, RAW panoramas, large video frames).
• You have a large undo history limit set (Preferences > Performance, History States).
• Your Mac's internal drive is already near capacity from other apps, system data, or old backups.
• Photoshop crashed during a previous session and left behind a multi-gigabyte temp file that was never cleaned up.

The last point is important. A clean quit removes the scratch file. A crash does not. Those orphaned files can take up several gigabytes and Photoshop will not remove them automatically the next time it starts.

How to Clear the Photoshop Scratch Disk While the App Is Open

The fastest way to reclaim scratch disk space without quitting is the Purge command.

Use Edit > Purge

1. In Photoshop, go to Edit in the menu bar.
2. Hover over Purge.
3. You will see four options: Undo, Clipboard, Histories, All. Select All to clear everything at once.

This immediately frees the RAM and scratch disk space used by your undo history and clipboard. Note that purging histories is not reversible: you will lose the ability to undo past actions in the current session. If you are in the middle of critical edits, save a version first.

For a rough estimate of how much scratch space is in use, look at the status bar at the bottom of any document window. Click the small arrow next to the file size readout and select Scratch Sizes. The right-hand number shows how much scratch disk space Photoshop is currently using.

How to Change or Add a Scratch Disk

If your startup disk is consistently tight, pointing Photoshop at a different volume gives it more breathing room.

1. Open Photoshop Preferences: Cmd + K, then click Scratch Disks in the sidebar.
2. Check or uncheck volumes. Photoshop will use them in the order listed.
3. Click OK and restart Photoshop for the change to take effect.

For best performance, choose the fastest available volume. An internal SSD will always outperform an external spinning hard drive.

You can also set the scratch disk at launch if Photoshop refuses to open at all. Hold Cmd + Option immediately after clicking the Photoshop icon in the Dock. A scratch disk picker dialog will appear before the app loads.

Finding and Deleting Orphaned Photoshop Temp Files

This is where a significant chunk of hidden space often hides. When Photoshop crashes, it abandons scratch files with names like Photoshop Temp1234567890 in your system's temporary folder.

Where Photoshop Temp Files Live on Mac

Photoshop scratch temp files are written to the macOS temporary directory. The exact path changes with each login session, but you can always reach it with this Terminal command:

open $TMPDIR

This opens the current temporary directory in Finder. Look for files or folders named Photoshop Temp followed by a string of digits. These are safe to delete when Photoshop is not running.

Some versions of Photoshop also write scratch files directly to the root of the selected scratch disk volume rather than the system temp folder. If you assigned a custom scratch disk, check its root level in Finder for any Photoshop Temp files as well.

Delete Them from Finder

1. Quit Photoshop completely.
2. Open Terminal and run open $TMPDIR.
3. In the Finder window that appears, look for any file or folder whose name starts with Photoshop Temp.
4. Drag those items to the Trash, then empty the Trash.

Delete Them from Terminal

If you prefer to do it in one step from Terminal (with Photoshop closed):

rm -rf $TMPDIR/Photoshop\ Temp*

Double-check that Photoshop is not running before executing this command. Deleting an active scratch file will corrupt the current Photoshop session.

Clearing the Photoshop Cache Folder

Separate from scratch files, Photoshop stores cache data in ~/Library/Caches. To clear it manually:

1. Quit Photoshop.
2. In Finder, press Cmd + Shift + G and paste: ~/Library/Caches
3. Look for folders named com.adobe.Photoshop or similar Adobe entries.
4. Move them to Trash and empty.

Photoshop will recreate these folders the next time it runs. You lose cached thumbnails so some documents may take slightly longer to render their previews on first open, but nothing is permanently affected.

Preventing the "Scratch Disks Are Full" Error Going Forward

• Keep at least 10-20 GB free on your scratch volume. Photoshop needs headroom, not just the space your current project requires. History states and clipboard use can multiply that footprint quickly.
• Reduce History States. In Preferences > Performance, the default is 50 history states. Dropping it to 20 significantly reduces scratch usage during long editing sessions.
• Disable Application Frame if you copy large bitmaps. Very large clipboard contents consume scratch space even when you don't think anything is on the clipboard. Purge the clipboard regularly during heavy sessions.
• Use Save As rather than Save for very large PSDs. Save As writes a fresh file, while Save incrementally appends data. Over many saves, this can bloat both the PSD and scratch usage.

Spotting Photoshop Temp Files Without Digging Through Folders

If your Mac's storage is being consumed by something you can't identify, those abandoned Photoshop Temp scratch files are a common culprit. They don't show up in the "Applications" or "Documents" breakdown in System Settings, so they can hide for months unnoticed.

Crumb scans the full volume including temp directories and flags stranded Photoshop Temp files specifically, so you can review exactly what you are looking at before removing it. It runs entirely on-device with no account required, which matters when your files include client work you would rather not route through a cloud service.

For most users, a combination of Photoshop's built-in Purge command and a periodic check of $TMPDIR in Finder is enough to keep scratch disk errors away. The key habit is simply quitting Photoshop cleanly after each session so it can remove its own temp files.