You're mid-edit, layers piling up, and then it hits: "Scratch Disk Full". You check your hard drive—there's 200GB free. You're furious. I know this error is infuriating, especially when the math doesn't add up.
This error usually pops up when you're doing heavy work: merging large panoramas, working with 16-bit files, or stacking dozens of layers. The trigger isn't always total disk space—it's about where Photoshop is allowed to write and how much it thinks it can use.
Root cause: It's not your free space, it's the limit
Photoshop uses your hard drive as virtual memory when RAM runs out. But here's the catch: on many systems, Photoshop has a hidden 2GB file size limit for scratch files (especially on older formats or certain drives). Even if you have terabytes free, that single file can't exceed the limit. So when it hits 2GB, boom—error.
Another common culprit: the scratch disk is set to your system drive (C: on Windows, Macintosh HD on macOS). That drive has less free space than your secondary drive, and other background processes (like Time Machine snapshots) eat into it unexpectedly. Photoshop checks the smallest free space across all assigned scratch disks, not the total.
The fix: Assign a dedicated scratch disk with room to breathe
- Open Preferences. Go to
Edit > Preferences > Scratch Diskson Windows, orPhotoshop > Settings > Scratch Diskson macOS. - Uncheck your system drive. Don't use C: or Macintosh HD as a scratch disk. It's the source of most headaches.
- Add a secondary drive. Pick your fastest internal SSD or an external drive with at least 100GB free. If you have multiple drives, assign them all—Photoshop will use them in order, and the error only triggers when all are full.
- Set the limit. In the same window, look for
Scratch Disk Size(Photoshop 2023+). Increase it to200GBor higher. This removes the 2GB cap. - Restart Photoshop. Scratch disk changes only take effect after a full restart. Don't skip this.
If you're on an older version (pre-2023)
You won't see the size limit option. In that case, the workaround is simpler: make sure the scratch disk has at least 50GB free, and close other apps that hog RAM. Also, consider clearing the Photoshop cache—it's not the scratch disk itself, but stale caches can confuse the disk-space calculation.
Windows: C:\Users\[YourName]\AppData\Local\Adobe\Photoshop\[Version]\
macOS: ~/Library/Application Support/Adobe/Photoshop/[Version]/Delete the Cache folder contents (keep the folder). That clears temporary files from failed renders. It's safe—Photoshop rebuilds them.
Still failing? Check these three things
- Is your drive actually writable? Permission issues can make a drive look free but block writes. Right-click the drive, get Info/Properties, and verify you have read/write access.
- Are you on an exFAT or FAT32 drive? These formats have a 4GB file size limit. Photoshop's scratch files can exceed that. Format the drive as NTFS (Windows) or APFS (macOS) instead.
- Is your RAM maxed? If you have 16GB or less, Photoshop hits the scratch disk hard and fast. Close Chrome, Spotify, and your 20 open tabs. In
Edit > Preferences > Performance, set Memory Usage to 80% for Photoshop only if you're not running other heavy apps.
The old "purge" trick—use it sparingly
If you're in the middle of a session and can't restart, go to Edit > Purge > All. This clears undo history and clipboard data, freeing up scratch space temporarily. It's a band-aid, not a fix. If you rely on it every session, you haven't set up your scratch disks properly.
Why I don't recommend third-party cleaners
Skip the "Photoshop cleaner" tools. They delete random cache folders and can break your preferences. The native settings are enough. I've seen more corrupted presets from those cleaners than from any real disk issue.
The real fix is giving Photoshop a dedicated scratch disk on a fast, non-system drive, and removing the size cap if you can. Do that, and this error becomes a rare nuisance rather than a daily interruption.
One last thing: if you're using a laptop with a single SSD, that's your constraint. In that case, keep 25% of the drive empty at all times, and consider upgrading RAM so Photoshop relies less on disk. It's not glamorous, but it works.