What a scratch disk is and why Photoshop fills it up

Photoshop uses a scratch disk — a section of your hard drive — as temporary storage when your computer's RAM runs out of space. When you work on large images or use memory-heavy filters, Photoshop writes data to this disk instead of keeping everything in RAM. If the scratch disk fills up completely, Photoshop stops working and shows an error message: "Could not complete your request because the scratch disk is full."

The scratch disk is not a separate physical drive — it is just free space on your existing hard drive. When that space runs out, Photoshop cannot save its temporary work, and you cannot continue editing. This happens most often when you are working with very large files, applying effects to high-resolution images, or running Photoshop alongside other programs that also use disk space.

Key Takeaways

  • Empty your Photoshop cache and temporary files through Edit > Purge to free up space immediately without closing the program.
  • Check how much free space your hard drive has — Photoshop typically needs at least 2 to 3 times the size of your image file available as scratch disk space.
  • Change your scratch disk to a different drive in Photoshop's preferences if your main drive is too full, or add an external drive as a secondary scratch disk.
  • Close other programs and delete old files from your Downloads and Desktop folders to create more free space on your hard drive.
  • Restart Photoshop after clearing the scratch disk so it can reset and use the newly available space.

Clear the scratch disk without closing Photoshop

The fastest way to free up space is to purge Photoshop's cache while the program is still open. This removes temporary data that Photoshop has stored but no longer needs. Open Photoshop and go to Edit in the menu bar, then hover over Purge. You will see four options: All, Undo, Clipboard, and Video Cache.

Click Purge > All to clear everything at once. This removes all undo history, the clipboard contents, and cached video data. You will lose the ability to undo your recent work, so save your current image first if you want to keep it. After you click All, Photoshop will free up whatever temporary space it was holding, and you can usually continue working immediately.

If you only want to clear specific types of cache, click Purge > Undo to remove undo history alone, or Purge > Clipboard to clear only what you have copied. Video Cache clears temporary video playback data if you work with video files. Start with Undo or Clipboard if you want to keep some undo steps, then use All if you need more space.

Check your hard drive's free space

Before you do anything else, find out how much free space you actually have. On Windows, open File Explorer, right-click your C: drive (or whichever drive Photoshop uses), and click Properties. Look at the pie chart — the blue section shows used space, and the white section shows free space. On Mac, click the Apple menu, select About This Mac, then click Storage. You will see a colored bar showing how much space is used and how much is free.

Photoshop needs at least 2 to 3 times the size of your image file as free scratch disk space. If you are working on a 500 MB image, you need at least 1 to 1.5 GB of free space. If your hard drive shows less than 10% free space (or less than 5 GB on a large drive), you do not have enough room for Photoshop to work properly, even after purging.

If your drive is nearly full, delete files you no longer need. Start with your Downloads folder, Desktop, and Recycle Bin (or Trash on Mac). Empty the Recycle Bin or Trash after deleting — files do not actually leave your drive until you empty it. You can also move large files like videos or old project folders to an external drive or cloud storage to free up space on your main drive.

Change your scratch disk to a different drive

If your main hard drive is too full but you have a second drive or external drive with plenty of space, you can tell Photoshop to use that drive instead. Open Photoshop and go to Edit > Preferences > Scratch Disks (on Windows) or Photoshop > Settings > Scratch Disks (on Mac). You will see a list of all drives connected to your computer, each with a checkbox.

The drive with a checkmark is your current scratch disk. Uncheck your main drive (usually C: on Windows or Macintosh HD on Mac), then check a different drive that has plenty of free space. You can select multiple drives — Photoshop will use them in order. Click OK, then restart Photoshop for the change to take effect.

If you use an external drive, make sure it is connected before you start Photoshop. External drives are slower than internal ones, so Photoshop may run more slowly, but it will work. Never use a USB flash drive as a scratch disk — they are too slow and can wear out quickly. A second internal drive or an external SSD (solid-state drive) works much better.

Close other programs to free up RAM

When your computer's RAM is full, Photoshop uses the scratch disk more heavily. Close programs you are not using — web browsers, email, music players, and other applications all take up RAM. The more RAM available, the less Photoshop has to write to the scratch disk, and the less likely you are to hit the full-disk error.

Check your system's RAM usage. On Windows, press Ctrl + Shift + Esc to open Task Manager, then click the Performance tab and look at Memory. On Mac, open Activity Monitor (in Applications > Utilities), click the Memory tab, and look at the Memory Pressure graph at the bottom. If Memory Pressure is in the yellow or red zone, close some programs.

If you regularly run out of scratch disk space, consider adding more RAM to your computer. Photoshop is memory-intensive, and upgrading from 8 GB to 16 GB or more makes a real difference, especially if you work with large files or use many filters at once.

Restart Photoshop and check the error is gone

After you have purged the cache, freed up hard drive space, or changed your scratch disk, close Photoshop completely and reopen it. This forces Photoshop to reset and recognize the newly available space. Do not just minimize it — actually quit the program.

Open your image again and try the action that caused the error. If you were applying a filter or effect when the error appeared, try it again now. If the error is gone, you have solved the problem. If it happens again, you may need to free up more space, use a larger scratch disk, or work with smaller images.

Prevent the scratch disk from filling up again

Keep your hard drive from getting too full by regularly deleting files you no longer need and moving large projects to external storage once they are finished. Set a habit of emptying your Downloads folder every month and archiving old Photoshop projects to an external drive or cloud storage.

If you work with very large files regularly, consider upgrading your hard drive to a larger capacity or adding a second drive dedicated to Photoshop work. You can also reduce the size of your images before opening them — if you are working on a 6000 x 4000 pixel image but only need 3000 x 2000, resize it first to use less scratch disk space.

Check your scratch disk settings occasionally. Go back to Edit > Preferences > Scratch Disks (Windows) or Photoshop > Settings > Scratch Disks (Mac) to make sure Photoshop is still using the drive you selected. If you added a new external drive, you can add it to the scratch disk list so Photoshop has more space to work with.

Frequently Asked Questions

Can I use my SSD as a scratch disk if my main drive is full?

Yes, if you have a second SSD or external SSD with free space, you can set it as your scratch disk in Photoshop's preferences. SSDs are much faster than traditional hard drives, so Photoshop will actually run faster using an external SSD than using a full internal drive. Make sure the SSD has at least 10 to 20 GB of free space.

What is the difference between purging Undo and purging All?

Purging Undo removes only your undo history, so you lose the ability to undo recent edits but keep your clipboard and video cache. Purging All removes everything — undo history, clipboard, and video cache — and frees up the most space. Use All if you need maximum space; use Undo if you want to keep some cache but free up a little room.

Why does Photoshop still say the scratch disk is full after I purged it?

Purging removes Photoshop's temporary cache, but if your hard drive itself is nearly full, you still do not have enough free space. Check your hard drive's free space in File Explorer or Storage settings. You may need to delete files from your computer or move them to external storage, not just purge Photoshop's cache.

Can I use a network drive or cloud storage as a scratch disk?

Network drives and cloud storage are too slow for Photoshop to use as a scratch disk — it will cause the program to freeze or crash. Use only a local drive: your internal hard drive, a second internal drive, or an external drive connected directly to your computer via USB or Thunderbolt.

How much free space should I keep on my hard drive?

Keep at least 10 to 15% of your hard drive free at all times. On a 500 GB drive, that means keeping at least 50 to 75 GB free. On a 1 TB drive, keep at least 100 to 150 GB free. This gives Photoshop and other programs room to work without constantly hitting the full-disk error.