"Scratch disks are full" in Photoshop on a Mac: the fixes

When Photoshop on a Mac says its scratch disks are full, the drive it uses for temporary working files has run out of free space. Photoshop works in memory, and when the memory it's allowed to use fills up, it writes to a scratch disk instead. Unless you've changed it, that's your startup disk, Macintosh HD.

Adobe's fixes come in a clear order. First, free up space: Adobe's current article says at least 100 GB on your primary scratch disk. Second, give Photoshop another drive in Photoshop › Settings › Scratch Disks, or hold down Command and Option as it starts if it won't open.

Third, make Photoshop store less, with fewer history states and Edit › Purge. Last, reset its preferences.

You don't need to hunt for Photoshop's temporary files. Adobe names them only on Windows, and on a Mac they're handled by Photoshop and macOS. If you ever do remove one, Photoshop must be quit first.

One more thing explains many puzzling cases. Finder counts purgeable space, such as Time Machine's local snapshots, as available, so a disk can look roomy while Photoshop still runs short. This post covers each fix, and how to see how much space is really free.

What a scratch disk is, and why Photoshop needs one

Adobe describes scratch disks as hard drives or SSDs that Photoshop uses for temporary storage when your computer's RAM isn't enough for what you're doing. It's Photoshop's own overflow space, separate from where your documents are saved.

How does Photoshop use the scratch disk?

Photoshop keeps the image you're editing, its layers and its undo history in memory, because memory is faster than any disk. Adobe's memory documentation says that when allocated memory fills up, Photoshop uses your drive as temporary virtual memory, the scratch disk, and performance drops.

It isn't only overflow from big images. Adobe says history states are kept in memory when possible, and when memory fills up, older history states move to the scratch disk.

How much memory does Photoshop use before the scratch disk?

By default, Adobe says, Photoshop claims 70% of available RAM and leaves 30% for macOS and other apps. You can change it in Photoshop › Settings › Performance with the Let Photoshop Use slider, and Adobe advises against going above 85%.

• Mac with 8 GB5.6 GB
• Mac with 16 GB11.2 GB
• Mac with 32 GB22.4 GB
• Mac with 64 GB44.8 GB

Calculated from Adobe's documented default of 70% of available RAM. Adobe's own examples give 5.6 GB for 8 GB of RAM and 44.8 GB for 64 GB. Available RAM can be a little lower than installed RAM.

Anything Photoshop needs beyond that goes to the scratch disk. On a Mac with less memory, the scratch disk gets used sooner and more.

What do the error messages mean?

Adobe lists three forms of the error. All of them mean the same thing: the scratch disk doesn't have enough free space for what Photoshop needs to write.

Message	When it appears	First thing to try
Could not initialize Photoshop because the scratch disks are full	At launch; Photoshop won't open	Free space, or Command-Option at launch
Could not complete your request because the scratch disks are full	During a task	Save, free space, purge
Scratch Disk Low	A popup at startup	Free space before you start work

Adobe adds that Photoshop may freeze, crash or refuse to launch, and that you may notice slower performance before the error appears.

Which drive is the scratch disk on a Mac?

Adobe's 2025 article says that by default Photoshop uses your internal OS drive as the scratch disk. On a Mac, that's the startup disk, and it's the same disk macOS, your apps and usually your files are on.

That's why the error is really about your whole Mac's free space. When the startup disk fills up, Photoshop is one of the first apps to complain, because it writes large temporary files quickly.

How much free space does Photoshop need?

Adobe's current article says to free up at least 100 GB on your primary scratch disk drive. The 2025 version recommended 50 GB free on your OS drive while working with Photoshop, and said more may be needed depending on your files.

On a 256 GB or 512 GB Mac, 100 GB is a lot to keep empty. If you can't, adding a fast external drive as a second scratch disk is the practical answer, covered below.

Is a scratch disk the same as macOS swap?

They work alike. macOS also moves memory to swap files on the startup disk when RAM runs short, and the catalog rates those swap files as managed by macOS. Photoshop's scratch disk is its own version of the same idea. The post on memory versus storage explains how the two relate.

Fix 1: free up space on the scratch disk

Adobe's first fix is the one that works every time: give the scratch disk more free space. For macOS, Adobe's article says to clean up your Macintosh HD drive or move files to an external drive, then restart Photoshop.

Where should you look first?

Open Apple menu › System Settings, click General, then Storage. The bar shows what's using the disk, and the recommendations below it can store files in iCloud, optimize storage and empty the Trash automatically.

Apple's advice for freeing space includes moving media to an external drive, deleting what you can download again, clearing out Downloads and removing apps you no longer use. The post on the "startup disk is almost full" warning goes through those steps.

Creative apps' own caches

If you also edit video, those apps are often the biggest single source of reclaimable space. Premiere Pro and After Effects keep a media cache in your Library that Adobe says is safe to clear, and DaVinci Resolve keeps a render cache, optimized media and proxies.

The posts on the Adobe media cache and DaVinci Resolve's cache and render files show how to clear each from inside the app.

Apps you no longer use

Apps themselves add up, especially creative suites with plug-ins and content libraries. The post on applications taking up space shows how to see which apps are largest and what to remove.

Where does space usually go on a creative Mac?

Every Mac is different, but on one used for photos and video, the same few places tend to hold most of what can go. This table lists them with the safe way to handle each.

Where	What it is	The safe way to reclaim it
~/Library/Application Support/Adobe/Common	Adobe's media cache	Premiere's Media Cache settings
Resolve's CacheClip folder	Render cache	Playback › Delete Render Cache
Finished projects and footage	Your work	Archive to an external drive
Photos library	Your photos	Photos' own Optimize Mac Storage
Downloads	Installers and files you saved	Review, then move to the Trash
Local snapshots	Time Machine's hourly snapshots	Let macOS remove them, or remove them now

Empty the Trash, then restart Photoshop

Files in the Trash still use space. Apple says storage doesn't become available until you empty the Trash. Empty it once you're sure, then quit and reopen Photoshop, as Adobe's steps say, so it checks the scratch disk again.

Fix 2: choose another scratch disk, or add one

If you have another drive, Photoshop can use it as well as, or instead of, the startup disk. Adobe calls this setting up additional scratch disks.

How do you set the scratch disks?

1. Choose Photoshop › Settings › Scratch Disks. In older versions the menu is called Preferences.
2. Select the drives you want Photoshop to use.
3. Use the arrow buttons to put them in order of priority, fastest first.
4. Click OK.

Adobe recommends choosing the fastest drives with the most free space. If you have only one drive, there's nothing else to choose, which is why freeing space comes first.

How do you change the scratch disk when Photoshop won't open?

Adobe documents a key combination for this. Hold down Command and Option while Photoshop launches, and the Scratch Disk Preferences dialog opens before anything else. Choose a drive with free space, then let Photoshop finish opening.

Connect an external drive before you try this, so it's in the list to choose.

Which drives can be a scratch disk?

Adobe lists the supported formats for scratch disks on macOS as APFS and Mac OS Extended (Journaled). ExFAT appears in Adobe's list only for Windows. A drive formatted for both Mac and Windows may therefore not suit a Mac scratch disk; the post on APFS versus exFAT explains how to tell and what reformatting means.

Drive	Scratch disk on a Mac?	Notes
Internal startup disk, APFS	Yes, the default	Shares space with macOS and your files
External SSD, APFS	Yes	Fast; the usual second scratch disk
External drive, Mac OS Extended (Journaled)	Yes	Supported by Adobe on macOS
External drive, exFAT	Not in Adobe's Mac list	Adobe lists exFAT for Windows only

Using an external SSD as a scratch disk

A fast external SSD is the simplest way to stop the error on a Mac with a small internal disk. Format it as APFS if only your Mac uses it, choose it in Scratch Disks, and move it to the top of the list.

Keep it connected while you work, since Photoshop writes to it constantly. The post on freeing up space with an external drive covers choosing a drive and what else can live on it.

Is a faster drive better?

Yes, for performance. Adobe recommends a fast internal SSD for Photoshop and its scratch disk where possible, and its scratch disk steps say to put the fastest drives first. Spinning hard drives and slow USB sticks make Photoshop slower whenever it spills onto them.

Fix 3: make Photoshop store less

Some settings change how much Photoshop needs to keep in memory and, in turn, write to the scratch disk. Adobe names several.

Purge what Photoshop holds

Choose Edit › Purge, then All to clear everything at once, or Undo, Clipboard, Histories or Video Cache on their own. Adobe says purging frees data Photoshop has built up for undo, the clipboard and other temporary operations, and that the Purge command can't be undone.

Save your document first if you might need to step back. After purging histories, earlier states are gone.

Lower the number of history states

Each history state is a step you can undo, and Adobe says each one uses memory according to how much of the image changed. The default is 50 and the maximum is 1,000.

To change it, open Photoshop › Settings › Performance and lower History States in the History & Cache section. Adobe suggests 20 to 30 to conserve memory.

Rethink auto-recovery for very large files

Adobe's 2025 article says turning off Automatically Save Recovery Information in Photoshop › Settings › File Handling reduces the size of Photoshop's temporary file, at the risk of having no auto-recovery. That's a real trade-off: a crash without recovery files can lose unsaved work.

If you keep it on, save often. If you turn it off, save even more often.

Check your document's units

Adobe's 2025 article mentions a less obvious cause: the wrong units when creating or resizing a document. A size typed in inches or centimetres instead of pixels can make a document vastly larger than you meant. Adobe suggests checking units when creating, resizing, cropping or changing the canvas size.

Bit depth, resolution and presets

Adobe says 16-bit and 32-bit images need much more memory, scratch space and processing time than 8-bit ones, and that higher resolutions increase scratch disk requirements too. It also says loaded presets such as brushes and patterns use memory and scratch disk space even when you aren't using them.

Converting to 8 bits per channel permanently deletes image data, so Adobe advises saving a copy of the original first. Lower resolution only where the final use allows it.

Setting	Where	Effect
Purge	Edit › Purge	Frees undo, clipboard, histories and video cache
History States	Settings › Performance	Fewer states, less to keep
Let Photoshop Use	Settings › Performance	More memory, less spill to disk, up to 85%
Automatically Save Recovery Information	Settings › File Handling	Off means a smaller temp file, no recovery
Image mode	Image › Mode	8-bit needs far less than 16 or 32-bit
Loaded presets	Preset panels	Fewer presets, less memory and scratch use

Watch the Efficiency indicator

Choose Efficiency from the pop-up menu at the bottom of a document window. Adobe says 100% means Photoshop is working entirely in memory, and anything lower means it's using the scratch disk. Below 90%, Adobe says performance degrades.

If Efficiency stays low during normal work, Adobe suggests raising Let Photoshop Use, up to 85%, or adding physical memory. Adobe also notes that on Apple silicon Macs, memory is shared between the processor and graphics, which makes using it efficiently even more important.

Cache levels and tile size

The History & Cache section of the Performance settings also has cache presets and a Cache Levels slider from 1 to 8. Adobe says higher levels make large, complex images redraw faster but use more memory, while levels 1 and 2 suit small documents with 50 or more layers.

If you mostly work on small files with many layers, a lower level leaves more memory for the image itself. Change one setting at a time and watch the Efficiency indicator.

Fix 4: reset Photoshop's preferences

Adobe's last fix is for a corrupted preferences file, which it says can affect how Photoshop handles scratch disks, often after a crash.

How do you reset them?

1. Quit Photoshop completely.
2. Hold down Shift, Option and Command while you open Photoshop.
3. Click Yes when asked to delete the Adobe Photoshop Settings file.
4. Set your scratch disks again in Photoshop › Settings › Scratch Disks.

When should you reset?

Adobe's 2025 article says that on rare occasions, when Photoshop or the Mac crashes, the preferences file can get corrupted and affect how Photoshop handles scratch disks. A reset is worth trying when the error keeps appearing although Disk Utility shows plenty of free space, or after a crash.

It's the last step for a reason. Try the first three fixes before you lose your settings.

What does a reset change?

Adobe says resetting returns all settings to their defaults. Workspaces, performance settings and the scratch disk list all go back to how they were when Photoshop was new, so note any settings you rely on before you reset.

Resetting preferences doesn't free disk space by itself; the file is small. It fixes Photoshop's handling of the scratch disk, which is a different problem from a full disk.

Photoshop's temporary files on a Mac

People searching for this error often find advice to dig out and delete Photoshop's temporary files. On a Mac, that's rarely needed and easy to get wrong.

Where are Photoshop's temporary files on a Mac?

Adobe's troubleshooting article names temporary files only for Windows, where they're files whose names begin with Photoshop Temp. For macOS, it says to clean up Macintosh HD or move files to an external drive, and doesn't name a folder.

Adobe Community Experts describe the Mac scratch file as living in macOS's own temporary folders on the startup disk, in randomly named folders, and in a hidden folder at the top of an external scratch disk. The catalog's entry for macOS's per-user temporary folders rates that area as managed by macOS.

When is it safe to remove them?

Only when Photoshop isn't running. While it's open, the scratch file is part of your work in progress. The catalog warns that removing files in macOS's temporary folders while apps use them can make those apps lose work or quit unexpectedly.

When Photoshop quits normally, Community Experts say it removes its scratch file. Either way, you rarely need to act: macOS removes temporary items that haven't been used for three days by default.

What about after a crash?

A crash or a force quit can leave a scratch file behind, according to Community Experts, who also note that permissions can stop you deleting it by hand. The catalog's advice for these folders is to leave them to macOS, which clears old temporary items on its own. Restarting Photoshop and quitting it normally is the gentlest next step.

Situation	What to do
Photoshop is open	Leave its temporary files alone
Photoshop quit normally	Nothing; its scratch file is gone
Photoshop crashed	Let macOS clear old temporary items
Scratch file on an external drive	Quit Photoshop; the hidden folder is managed the same way

Why free space can look bigger than Photoshop sees

A common puzzle: Finder says there's plenty of space, and Photoshop still says the scratch disk is full. Usually, the difference is purgeable space.

Purgeable space

Purgeable space is storage macOS says it can free by itself when something needs it. Finder counts it as available. The guide to purgeable space explains what's in it and why a large write can still fail: macOS frees it when asked, but not always as fast as the request arrives.

Adobe doesn't document how Photoshop measures free space on a scratch disk. If Photoshop and Finder disagree, check the free figure without purgeable space, as below.

Time Machine's local snapshots

Much of what's purgeable on many Macs is Time Machine's local snapshots. Apple says your Mac counts the space they use as available storage, and Time Machine removes them as they age or as space is needed.

When you edit large image files, snapshots can hold on to old versions of them, which takes more space. The post on Time Machine taking up space explains how to see and remove them.

How do you see how much is really free?

Open Disk Utility, select your startup disk's volume, and look at its figures: Disk Utility shows used, purgeable and free space separately. The post on using Disk Utility to read your storage explains each number.

Where you look	Figure shown	Includes purgeable?
Finder window or Get Info	Available	Yes
System Settings › General › Storage	Used and available	Yes, counted as available
Disk Utility	Used, purgeable and free	Shown separately

What should you do when the numbers disagree?

Wait a minute and try again, since macOS may have freed purgeable space in the meantime. If it keeps happening, remove local snapshots now rather than waiting, or free real space as in Fix 1. A second scratch disk on an external drive avoids the question entirely.

Keeping the error from coming back

Once the error is fixed, a few habits keep Photoshop's demands on the scratch disk down. They all come from how Adobe says Photoshop uses memory.

How many documents do you keep open?

Adobe says working with several open documents at once multiplies memory demands. Each one keeps its own image data and history. Closing documents you've finished with gives Photoshop room again, and less spills onto the scratch disk.

The kind of edit matters too. Adobe compares a filter applied to a whole 8000 by 6000 pixel layer with the Healing Brush on a small area: the full-image operation needs far more memory and storage.

Do Smart Objects use more memory?

Yes. Adobe says Photoshop keeps both the embedded source file and the rendered result of each Smart Object in memory. Its example: a document with ten Smart Objects effectively loads eleven complete images, the composite plus each Smart Object's source.

Smart Objects are worth it for flexible editing. When a document grows heavy, rasterizing the ones you won't edit again reduces the load, but only after you've saved a copy with them intact.

Do other Adobe apps running at the same time matter?

They can. Adobe's documentation for After Effects and Media Encoder says those apps share a memory pool with Photoshop, Premiere and Audition, with a balancer that shares memory among the apps that are running. The more of them are open, the less each one gets.

If you move between Photoshop and a video app, quitting the one you aren't using leaves more memory for the other, and less work for its scratch disk.

Which file format suits very large images?

Adobe lists the limits. PSD files are limited to 2 GB, TIFF files to 4 GB, and PSB, Photoshop's Large Document Format, supports far larger files. Documents that grow past 2 GB need PSB, and they'll need scratch space to match.

Saved files take space on disk too. Adobe says setting Maximize PSD and PSB File Compatibility in File Handling to Ask or Never reduces file size and saves time, though older apps may then not open your files.

How much memory should a Mac for Photoshop have?

Adobe says to use at least 8 GB of RAM and recommends 16 GB or more for current desktop versions of Photoshop. If Efficiency stays low even at 80 to 85% allocation, Adobe says more physical memory helps more than a higher percentage.

Memory and disk work together here: the less memory Photoshop has, the more it writes to the scratch disk, and the more free space it needs.

Mistakes to avoid, and a worked example

Mistakes to avoid

• Deleting temporary files while Photoshop is open. That's your work in progress.
• Pasting cleanup commands from the web. They delete without the Trash and can remove files apps are using.
• Picking an exFAT drive as a scratch disk. Adobe lists only APFS and Mac OS Extended for Mac scratch disks.
• Setting Let Photoshop Use above 85%. Adobe says it rarely helps and can make your Mac unstable.
• Purging before saving. Purged histories can't come back.
• Expecting a cache clear to speed up your Mac. Freeing space fixes the error; it doesn't make your Mac faster.
• Forgetting the Trash. Deleted files free nothing until it's emptied.

A worked example: a 512 GB MacBook Air

Say a photographer edits large layered files on a 512 GB MacBook Air with 16 GB of memory, and Photoshop starts saying "Scratch Disk Low" at launch. Following Adobe's order:

1. They open System Settings › General › Storage and find old video projects and an Adobe media cache in their Library taking much of the space.
2. They clear the media cache from Premiere's Media Cache settings and move finished projects to an external drive.
3. They empty the Trash and check Disk Utility, which shows the free space without purgeable space.
4. They format a fast external SSD as APFS and add it as the first scratch disk in Photoshop › Settings › Scratch Disks.
5. They lower History States to 30 and leave Let Photoshop Use at the default.

The error stops because there's real free space on both scratch disks. The Efficiency indicator still dips on their largest files, which is the sign that more memory, not more disk, would help next.

When the error comes back

If the error returns soon after you've freed space, something else on the startup disk is growing. Video caches, snapshots and downloads are the usual suspects, and finding them is the same job as for any full disk.

Three checks narrow it down:

• Storage settings shows which category grew since you last looked.
• Disk Utility shows whether the space is really used or only purgeable.
• The Efficiency indicator shows whether Photoshop is leaning on the scratch disk more than before, which points to memory rather than disk.

How the app does it

Wombit shows what's using your startup disk, so you can see why the scratch disk filled up: the map shows every folder by size, with an explanation for each item from a catalog written and checked by hand. Its space meter, in the app and in the menu bar, shows the available space honestly, beside what's truly free.

The catalog explains the things that often fill a creative Mac, such as Adobe's media cache, which is Safe and starts checked in Cleanup. macOS's temporary folders and Time Machine's local snapshots are Managed by macOS: explained, and left to macOS's own mechanism, never moved.

• ~/Library/Application Support/Adobe/Common/{Media Cache Files,Media Cache}

  Adobe media cache

  Conformed audio, peak and index files that Premiere Pro and other Adobe video apps create for imported media.

  Safe · Moves it to the Trash

• /private/var/folders

  Per-user temporary files and caches

  Private temporary folders and caches that macOS creates for each user account, in hidden folders with random names.

  Managed by macOS · Explained only: never removed

• Time Machine local snapshots

  Hourly snapshots of your startup disk that Time Machine keeps on the disk itself, so you can restore files even without your backup disk.

  Managed by macOS · Runs tmutil for Time Machine's own snapshots, through the helper

File names and paths never leave your Mac, and everything Cleanup moves goes to the Trash, with Undo and Put Back.

The analyzer, the map, the explanations and the space meter are free. Cleanup and Time Machine snapshots are PRO: one payment of $4.99 with lifetime access. Every Pro tool's review is free to open, so you see what would go and why before you buy.