What Is Purgeable Space on Mac? (And How to See What's In It)

You delete a 30GB file and Storage settings says you have 30GB more available. Then nothing changes for a few days. Then suddenly 5GB more appears. Then 20GB disappears overnight. Welcome to APFS purgeable space — the part of your Mac’s storage Apple manages without telling you, and which makes Mac storage accounting genuinely confusing.

This guide breaks down what purgeable means, what’s in it, how to see the contents, and what (if anything) you can do about it.

The 30-second explanation

macOS keeps certain files locally that it could delete to free space. They’re useful — caches, snapshots, downloaded copies of cloud files — but not strictly necessary. Apple calls these “purgeable.”

When Storage settings shows free space, it INCLUDES purgeable as available. So a Mac that’s “256GB used / 244GB available” might actually be 280GB used with 30GB of that being purgeable. The numbers represent what macOS will give you, not what’s really free.

When something requests more space, macOS purges in priority order until enough is freed. To you, it just looks like space appeared.

What’s classified as purgeable

The main categories:

Time Machine local snapshots. macOS keeps hourly snapshots of your drive on the internal SSD for up to 24 hours, separate from your external Time Machine drive. These can be 5-30GB.

iCloud Drive files when “Optimize Mac Storage” is on. Files that exist in iCloud and have local copies become purgeable — macOS can offload to make room.

iCloud Photos. Same idea. Photos with originals in iCloud and previews locally are purgeable.

Downloaded TV/movies in TV.app. With “Automatically delete watched movies” enabled, watched content is purgeable.

Some app caches. macOS knows certain caches can be safely cleared.

Unused Apple media. Mail attachments downloaded but not opened, podcast downloads in completed shows, etc.

Localizations. Language files for languages you never use can be marked purgeable for native Apple apps.

How to see your purgeable space

System Settings → General → Storage shows total usage but doesn’t break out purgeable in current macOS versions. To see the actual purgeable number:

diskutil info / | grep -i "Free Space"

Compare with:

df -h /

The gap between filesystem-reported free space and Storage’s “available” number is roughly purgeable.

Or, the more direct way:

diskutil apfs list

Look for “Purgeable” lines under each volume. Numbers in GB appear there.

For a specific volume:

diskutil info /Volumes/Macintosh\ HD

Shows detailed info including purgeable estimate.

Why this exists

Apple’s reasoning: most users don’t want to manage what’s local versus what’s cloud. They want their files when they need them, and they want enough free space when they need that. Purgeable is the mechanism for both.

The downside: it’s opaque. Tools like df and du give different answers because they’re measuring different things. Storage settings shows numbers that include purgeable as “free” but may not be free in the next minute if something requests space.

For most users, this works invisibly. For people trying to manage storage carefully, it’s frustrating.

Time Machine local snapshots

The biggest purgeable category for most users. List them:

tmutil listlocalsnapshots /

You’ll see entries dated by hour. macOS holds these for up to 24 hours, automatically purging older ones.

Check size:

sudo tmutil listbackups

(That lists external Time Machine backups, but related.)

To force snapshot thinning:

tmutil thinlocalsnapshots / 999999999999 4

That asks macOS to thin aggressively, requesting up to 999999999999 bytes free with priority level 4 (most aggressive).

To delete a specific snapshot:

sudo tmutil deletelocalsnapshots [date-string-from-list]

After thinning, snapshots regenerate during normal use, but the immediate space comes back.

iCloud-related purgeable

If you have Optimize Mac Storage on, iCloud Drive files contribute to purgeable.

Check size of iCloud Drive locally:

du -sh ~/Library/Mobile\ Documents/com~apple~CloudDocs

To see what’s offloaded already (placeholders):

find ~/Library/Mobile\ Documents -type f -name ".*.icloud" 2>/dev/null | wc -l

That counts cloud-only placeholders.

To force more iCloud offloading manually:

brctl evict /path/to/file

Or right-click in Finder → Remove Download.

For Photos library purgeable:

Open Photos. Photos → Settings → iCloud. Verify “Optimize Mac Storage” is checked. Photos library shows total in iCloud size — local size is much smaller when optimized.

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What you actually can’t reclaim manually

Some purgeable categories aren’t user-controllable. macOS handles them on its schedule.

Mail attachments — Mail.app stores attachments locally for offline access. macOS purges as needed.

Localizations — Language files for unused languages on Apple system apps. Apple decides.

System caches macOS calls purgeable — Various system-managed caches.

For these, the best you can do is wait for macOS to purge under pressure.

When Storage settings lies

You’ll occasionally see Storage settings claim 50GB free when df says 10GB. The 40GB difference is purgeable.

Try copying a 30GB file. macOS will purge as needed and make room. But if you check Storage immediately after, the new file’s space comes from purgeable, not from old free space.

This is why people sometimes complain “I deleted 20GB but my Mac shows the same available space.” macOS rebalanced — your deletion freed actual space, but purgeable expanded to match, keeping the “available” number the same.

The net effect is typically that you DO have access to space when you need it. The accounting just doesn’t match intuition.

Diagnosing storage with command-line tools

For accurate accounting that ignores purgeable:

df -k / | tail -1 | awk '{print "Used: " $3/1024/1024 " GB, Available: " $4/1024/1024 " GB"}'

That gives raw filesystem numbers. “Available” here is real free space, not including purgeable.

For total used by a user:

sudo du -sh /Users/[username] 2>/dev/null

For top-level directories sorted by size:

sudo du -sh /* 2>/dev/null | sort -hr | head -20

These show actual disk usage, ignoring the purgeable abstraction.

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When purgeable becomes a problem

Purgeable is mostly invisible benefit. The exceptions:

You’re trying to install a large game or application. macOS can purge as needed, but if the game wants 100GB and you have 80GB free + 20GB purgeable, the install should work. Sometimes it stalls because the purge is slow.

You’re booting from a backup. Time Machine restores need actual free space, not purgeable.

You’re using disk imaging tools. Some third-party tools don’t understand purgeable and get confused.

You’re cloning to a smaller disk. The destination needs to fit actual data, but tools may report misleading source size.

You’re troubleshooting weird “out of space” errors. Sometimes purgeable hits its limits and macOS refuses to purge fast enough.

For these, you may need to force a manual purge of snapshots and offload what you can.

Forcing a full purge

For maximum reclamation:

sudo tmutil thinlocalsnapshots / 999999999999 4

brctl evict ~/Library/Mobile\ Documents/com~apple~CloudDocs/* 2>/dev/null

sudo find /private/var/db/diagnostics -type f -mtime +30 -delete 2>/dev/null

Empty trash (Trash itself is treated specially):

osascript -e 'tell application "Finder" to empty trash'

After running these, give macOS a few minutes to update Storage settings. Available space should expand.

The mental model that works

Stop thinking of Mac storage as “X GB used, Y GB free.” Think of it as:

• My data: The files I created or actively store
• System data: What macOS needs (kernel, apps, settings)
• Purgeable: What macOS could let go of

Storage settings shows your total, with purgeable counted as available. df shows raw filesystem state, with purgeable counted as used.

Both are valid views. Knowing both helps you understand why numbers differ across tools.

What the typical Mac has

Rough numbers from real Macs:

• Light user, 256GB SSD: 5-10GB purgeable (mostly Time Machine snapshots)
• iCloud-heavy user, 512GB: 20-50GB purgeable (iCloud offload candidates)
• Heavy user, 1TB: 30-80GB purgeable (snapshots + iCloud + caches)

If your purgeable is way outside these ranges (300GB+), something might be wrong. Usually it’s stuck Time Machine snapshots that aren’t thinning, or iCloud sync errors.

For most people, purgeable is fine to leave alone. macOS handles it. Knowing it exists helps you understand the storage numbers you see — but actively managing it is rarely necessary.

The exception: when something specific is wrong, knowing how to force purges and check actual filesystem state lets you fix what macOS’s automatic systems aren’t fixing on their own.