"Scratch disks are full" — the Photoshop error that stops everything

Updated September 2026 · 6 min read

You're in the middle of a project, and Photoshop freezes with a dialog: "Could not complete your request because the scratch disks are full." Sometimes it won't even launch. The error feels mysterious, but the cause is simple: your Mac ran out of space where Photoshop writes its temporary working files.

Here's how to fix it right now and how to make sure it doesn't happen again.

What is a scratch disk?

When you work on large files, Photoshop needs more space than your RAM can provide. It uses your hard drive as overflow — that's the scratch disk. By default, it's your startup disk (the same drive where macOS lives). When that drive fills up, Photoshop has nowhere to write and crashes.

The scratch disk isn't a special partition. It's just regular free space on your drive. So "scratch disk full" really means "your Mac's disk is full" — or close enough that Photoshop can't get the room it needs.

Quick fix: free up space immediately

If Photoshop won't even open, you need to clear space before anything else. The fastest wins:

Empty the Trash. Right-click the Trash icon and select Empty Trash. People forget — files in Trash still take up space.
Clear Photoshop's own temp files. Navigate to /tmp in Finder (Go → Go to Folder → type /tmp). Look for files starting with Photoshop Temp. These are scratch files from previous sessions — if Photoshop crashed without cleaning up, they can be massive. Delete them.
Delete old downloads. Open your Downloads folder, sort by size, and remove anything you no longer need.
Clear app caches. ~/Library/Caches often contains gigabytes of browser cache and other app junk that rebuilds automatically.

Once you've freed a few GB, try opening Photoshop again. If it launches, you can fix things properly from inside the app.

Change your scratch disk location

If your startup disk is always tight on space, tell Photoshop to use a different drive:

Open Photoshop → Preferences → Scratch Disks
Check the box next to a drive with more free space (an external SSD works well)
Uncheck your startup disk if you want to avoid this problem entirely
Restart Photoshop

If Photoshop won't launch at all, hold Cmd+Option immediately after clicking the Photoshop icon. This opens the scratch disk preferences dialog before the app fully loads, letting you switch drives even when you can't get in.

Purge from inside Photoshop

Once Photoshop is running, you can free up scratch space without closing your file:

Go to Edit → Purge → All. This clears the clipboard, undo history, and cached data from memory and scratch. You'll lose your undo states for the current session, but it can free several GB instantly.

Reduce Photoshop's scratch demand

Some habits make Photoshop hungrier than it needs to be:

Too many history states. Preferences → Performance → History States. The default is 50. Each state for a large file can use hundreds of MB. Dropping to 20 dramatically reduces scratch usage.
Too many open files. Every open document uses scratch space. Close files you're not actively editing.
Large clipboard. If you copied a huge image, it lives on the scratch disk until you copy something else. Edit → Purge → Clipboard frees it.

The real problem: your Mac is full

The scratch disk error is a symptom, not the disease. If your startup disk is regularly below 10–15% free, every app will struggle — not just Photoshop. macOS itself needs free space for virtual memory, updates, and system functions.

For a deeper cleanup beyond Photoshop, clearing all Adobe caches is a good next step — media caches from Premiere Pro and After Effects can silently consume 20–50 GB.

Keep your disk healthy automatically

Gigatidy monitors your Mac's free space, finds the biggest space wasters, and helps you clean them before you hit errors like this.

Meet Gigatidy →

FAQ

Can I use an external drive as a Photoshop scratch disk?

Yes, and it's one of the best solutions if your internal drive is small. Use an SSD — a spinning hard drive will make Photoshop noticeably slower. Set it in Preferences → Scratch Disks.

Why does "scratch disks are full" happen when I still have free space?

Photoshop needs contiguous free space, and it may need more than what's technically available. If your disk is 90%+ full, the remaining fragments may not be enough. Also, Photoshop reserves space beyond what your file alone needs — for undo history, clipboard, and working data.

Will Photoshop automatically clean scratch files when I close it?

Under normal circumstances, yes. When you quit Photoshop properly, it deletes its temp files. But if Photoshop crashes or you force-quit it, those temp files can be left behind in /tmp and won't be cleaned until you manually remove them or restart your Mac.