That little popup in the corner of your screen reading “Your disk is almost full” is one of the most common alerts a Mac owner will ever see. I have hit it on three different Macs in our household, and every time it felt like a small emergency. The good news is that in most cases you can reclaim several gigabytes in under an hour without buying anything. This guide walks through how to free up storage when your Mac startup disk is almost full, step by step, starting with the fastest actions and finishing with recovery options for disks so packed the Mac will not even boot.
I will cover what the startup disk actually is, how to check which files are eating your space, and the cleanup order our team has found to work best across macOS Ventura, Sonoma, Sequoia, and the versions still rolling out in 2026. You will also learn what the mysterious “System Data” category really contains, how to use macOS built-in storage tools, and what to do when your Mac is so full it refuses to start. By the end you should have a clear, ordered plan instead of a long list of random tips.
One quick note before we start: keep at least 20 GB of free space available if you can. macOS uses free disk space for virtual memory, system caches, and software updates. When that buffer disappears, the whole machine slows down and updates begin failing.
Free up storage when your Mac startup disk is almost full by tackling the fastest wins first
The most effective approach is to work from quick, low-risk actions toward deeper cleanup. Emptying the Trash, clearing the Downloads folder, and removing old iOS backups together often reclaim 10 to 50 GB in a single session. From there you can move on to deleting unused apps, trimming System Data, and shifting large media files to external or cloud storage.
I recommend running through the steps in the order below, because each one takes a different amount of time and returns a different amount of space. You can stop as soon as you have a comfortable buffer, or continue to the deeper steps if your disk is critically full.
| Cleanup Method | Typical Time | Space You Can Reclaim | Risk Level |
|---|---|---|---|
| Empty Trash and Downloads | 2 minutes | 1 to 20 GB | Low |
| Delete old iOS backups | 5 minutes | 5 to 40 GB | Low |
| Uninstall unused apps | 10 minutes | 2 to 15 GB | Low |
| Clear user caches and logs | 15 minutes | 1 to 10 GB | Medium |
| Remove Time Machine local snapshots | 5 minutes | 5 to 50 GB | Low |
| Move large media to external drive | 30 to 60 minutes | 20 to 200 GB | Low |
| Safe Mode cache flush | 15 minutes | 1 to 5 GB | Low |
| Recovery Mode file deletion | 30 minutes | Varies | Higher |
Read on for exact steps for each method, plus what to do when the warning refuses to go away.
A startup disk is the main storage drive that holds macOS and your files
Your startup disk is the storage volume macOS boots from, almost always named Macintosh HD on a factory Mac. It holds the operating system, your applications, your user folders, and all of the hidden support files macOS creates as you work. When you see the “Your disk is almost full” message, macOS is telling you that this specific volume has less than about 15 percent of its total capacity left.
On modern Macs the startup disk is an SSD soldered to the logic board, which means you cannot simply swap a larger drive. That makes regular cleanup more important than it was on older Macs with replaceable hard drives. External drives, cloud storage, and a lean set of installed apps are your main tools for long-term management.
Do not confuse the startup disk with secondary volumes you may have created with Disk Utility, or with external drives you use for Time Machine. Only the boot volume triggers the low-space warning. You can confirm which disk is the startup disk by opening System Settings, clicking General, then About, and reading the “Startup disk” line.
A full startup disk does more than trigger an annoying popup. It blocks macOS updates, slows the system because there is no room for virtual memory swap files, causes apps to crash when they cannot write temporary data, and in extreme cases stops the Mac from booting at all. Clearing space fixes all of these symptoms at once.
Check your Mac disk space in System Settings or About This Mac before deleting anything
Before you start removing files, take a minute to see exactly what is consuming your space. macOS shows a color-coded storage bar that breaks usage into categories like Apps, Documents, System Data, and macOS. This tells you where to focus your cleanup effort.
On macOS Ventura, Sonoma, Sequoia, and later: open System Settings
Click the Apple menu, choose System Settings, then click General in the left sidebar. Select Storage. After a few seconds you will see a colored bar and a list of categories with the space each one occupies. Click the “i” button next to Documents, Applications, or Messages to jump straight to those files.
On macOS Monterey and earlier: use About This Mac
Click the Apple menu, choose About This Mac, then click the Storage tab. Hover over each colored segment to see its name and size. Click Manage to open the older Storage Management window with built-in recommendations.
Read the storage bar with realistic expectations
The bar updates slowly because macOS scans every file, so give it a minute. The biggest segments are usually Documents, Apps, Photos, and System Data. If System Data is the largest block, plan to spend extra time on the cache and snapshot steps later in this guide.
Note the number of gigabytes shown as available before you start. I write it down so I can measure how much space each step actually returns. That feedback helps you decide when to stop cleaning.
Empty the Trash and Downloads folder first to recover space in minutes
This is the single fastest fix and it almost always returns at least a few gigabytes. Files you delete on a Mac are not actually removed until the Trash is emptied, so months of discarded items can sit there quietly using space.
Step 1: Empty the Trash from the Dock
Click and hold the Trash icon in the Dock, then choose Empty Trash. Confirm the prompt. If you have multiple drives, also empty the trash on any external volumes by opening them in Finder and using the same command, because each volume keeps its own hidden .Trashes folder.
Step 2: Sort the Downloads folder by size
Open Finder, click Downloads in the sidebar, and switch to list view. Choose View, then Show View Options, and turn on Calculate all sizes. Click the Size column header to sort largest first. Most people find disk images, installer packages, and zip archives they forgot about, often totaling 5 to 20 GB.
Step 3: Clear the hidden Mail Downloads folder
Every time you open an attachment in Mail, macOS saves a copy to a folder called Mail Downloads inside your user Library. I have seen this folder reach 30 GB on Macs used for years of email. Open Finder, press Shift-Command-G, type ~/Library/Containers/com.apple.Mail/Data/Library/Mail Downloads, and delete the contents.
After emptying the Trash again, check the storage bar. In my experience this single pair of steps frees 3 to 20 GB for most users.
Delete old iOS backups and iTunes files that can exceed 20 GB
If you have ever backed up an iPhone or iPad to your Mac, those backups live on your startup disk and can be enormous. A single full iPhone backup of a 256 GB device can consume 60 GB or more, and old backups are rarely needed once you have moved to iCloud backup.
Manage backups in Finder on macOS Catalina and later
Open Finder, connect your device if you still have it, and select it in the sidebar under Locations. In the General or Backups section, click Manage Backups. You will see a list of every backup stored on this Mac, with dates. Select backups for devices you no longer own and click Delete Backup. Repeat for any backup older than your current phone.
Find backups directly in the Library folder
If you no longer have the device, you can still remove its backup manually. Press Shift-Command-G in Finder, enter ~/Library/Application Support/MobileSync/Backup, and you will see folders named with long strings of characters. Each folder is one device backup. Sort by date modified to identify stale ones, then drag them to the Trash.
Remove old iOS software update files
iTunes and the Finder-based sync also download IPSW software update files that can be several gigabytes each. Look in ~/Library/iTunes/iPhone Software Updates and ~/Library/iTunes/iPad Software Updates and delete everything inside. These files are downloaded fresh whenever they are needed, so they are safe to remove.
On a Mac that has synced several iPhones over the years, this section alone often clears 20 to 80 GB. I rank it second only to media offloading for total space returned.
Uninstall apps you no longer use through Finder or Launchpad
Applications and their support files add up quickly. A single creative suite can occupy 15 GB, and games regularly exceed 50 GB. Removing titles you have not opened in months is one of the most reliable ways to claw back serious space.
Delete App Store apps from Launchpad
Open Launchpad, click and hold any icon until they jiggle, then click the X on apps you want to remove. This works for apps installed from the Mac App Store and fully removes them in one step.
Drag non-App-Store apps from the Applications folder
Open the Applications folder in Finder, then drag unwanted apps to the Trash. Apps downloaded from developer websites, like older versions of Adobe or Microsoft products, are removed this way. Empty the Trash afterward.
Clean up leftover support files in your user Library
Dragging an app to the Trash leaves behind preference files, caches, and application support folders. Press Shift-Command-G, enter ~/Library, and check these three subfolders for remnants of the app you removed: Application Support, Caches, and Preferences. Look for folders named after the developer or the app, then move them to the Trash.
Be careful in the Library folder. Only delete folders you clearly recognize as belonging to the app you just uninstalled. When in doubt, leave it alone. I once deleted a shared framework folder and had to reinstall an unrelated app to fix the resulting crash.
System Data and Other storage contain caches, logs, language files, and Time Machine snapshots
The “System Data” category, called “Other” on older macOS versions, is the gray block that frustrates everyone. It is not one thing. It is a catch-all for files macOS cannot sort into the tidy categories like Apps or Photos. On most Macs it grows to 30 to 80 GB over a couple of years of use.
Inside System Data you will find user and system caches, log files, language resource files for apps you use in only one language, screen savers and desktop pictures, Mail downloads, Time Machine local snapshots, and various plug-ins. None of these are your personal documents, which is why the category feels invisible.
Understand purgeable space
macOS sometimes marks part of your available space as “purgeable.” This is space the system considers free and will automatically delete when an app needs it, typically containing locally stored iCloud files, Time Machine snapshots, and recently watched TV shows. You do not normally need to remove purgeable files manually; the system handles it. But if your reported free space is lower than expected, purgeable content may be the reason.
Why System Data grows over time
Caches accumulate because apps store downloaded content locally to load faster next time. Logs record system and app events for troubleshooting. Time Machine creates hourly local snapshots so you can restore files even when your backup drive is disconnected. None of this is broken behavior, but together it explains the steady creep.
Phantom space consumption, the situation where free space vanishes with no obvious cause, is almost always snapshots or caches. Our team has traced 40 GB of missing space to Time Machine snapshots alone on a Mac that had not been connected to its backup drive in weeks.
Clear cache files and log files when they grow beyond a few gigabytes
Cache files exist to speed up your Mac, so macOS rebuilds them as needed. Deleting user caches is safe and often returns several gigabytes, especially on Macs that have been upgraded through multiple major macOS versions.
Clear user caches safely
Press Shift-Command-G in Finder, type ~/Library/Caches, and press Return. You will see folders named after your applications. Select all of them, drag them to the Trash, and empty it. Do not delete the Caches folder itself, only its contents. Apps will recreate the folders they need the next time they run.
Clear system caches with care
Open the Go to Folder dialog again and enter /Library/Caches (without the tilde). This is the system-wide caches folder. You can delete its contents, but skip anything currently in use, which macOS will tell you by showing a lock icon or an “in use” error. When in doubt, restart the Mac first.
Trim down log files
Log files live in ~/Library/Logs and /Library/Logs. These accumulate crash reports, install logs, and diagnostic data. You can safely delete the contents of both folders. The system and apps will start fresh logs immediately. On a heavily used Mac this can reclaim 1 to 5 GB.
Remove unused language resources
Every application ships with localization files for dozens of languages you probably do not use. These .lproj folders sit inside each app bundle. Removing the ones you do not need can save 500 MB to 2 GB across all your apps. This is an advanced step, so only attempt it on apps you can easily reinstall, and never touch the English or your native language .lproj folder.
Restart your Mac after any cache or log cleanup. This flushes memory, finalizes deletions, and lets you see the true free-space figure on the storage bar.
Remove Time Machine local snapshots to reclaim hidden space
Time Machine creates hourly local snapshots on your startup disk so you can recover deleted files even when your external backup drive is unplugged. macOS is supposed to delete old snapshots automatically when space gets tight, but this does not always happen promptly, and snapshots can quietly consume 20 to 50 GB.
See your local snapshots in Terminal
Open Terminal from Applications, Utilities. Type tmutil listlocalsnapshots / and press Return. You will see a list of snapshot dates. Each one is a point-in-time copy that takes up space on your disk.
Let macOS thin them automatically
The simplest fix is to connect your Time Machine drive and let a backup complete. Once the data is safely on the external drive, macOS becomes more willing to delete local snapshots. If you do not have the drive handy, you can trigger cleanup with the command tmutil thinlocalsnapshots / 10000000000 4, which asks the system to thin snapshots down to roughly 10 GB.
Delete individual snapshots if needed
To remove a specific snapshot, run tmutil deletelocalsnapshots followed by the snapshot date string from the list command. For example: tmutil deletelocalsnapshots 2024-06-15-002341. Repeat for each snapshot you want gone. This is one of the most effective fixes for “phantom” space consumption.
On Macs that travel without their backup drive for weeks, snapshots are the number one cause of mysterious space loss. I check this first whenever a user reports free space shrinking with no obvious cause.
Move large files to an external drive or iCloud instead of keeping them on the startup disk
Once you have cleared the easy wins, the next biggest target is your own media. Video projects, raw photo libraries, music collections, and virtual machine images are the usual suspects, and they are often the reason the disk filled up in the first place.
Find the largest files with a Finder search
Open a Finder window, press Command-F, and set the search criteria to “File size” is greater than, then enter 1 GB. Sort the results by size. You will quickly see which videos, disk images, and project archives are worth relocating.
Move libraries to an external SSD
Photos, Final Cut Pro libraries, and Logic Pro sound libraries all support being stored on an external drive. Quit the app, move the library file to a fast external SSD formatted as APFS, then double-click the moved library to open it in the future. A single large video project can free 50 to 200 GB this way.
Use iCloud Drive with Optimize Mac Storage
Open System Settings, click your Apple ID, then iCloud. Turn on iCloud Drive and enable “Optimize Mac Storage.” macOS will then store older files only in iCloud and download them on demand when you open them. This keeps recent files local and pushes the rest to the cloud, freeing potentially hundreds of gigabytes.
Archive the Desktop and Documents folders
If you enabled the Desktop and Documents folders in iCloud, those folders sync fully and can balloon your local storage. Review them, move anything older than a year to an external drive, and delete what you no longer need. Our team treats the Desktop as a temporary workspace and archives it monthly.
Use Storage Management and Optimize Storage tools built into macOS
macOS ships with a built-in storage assistant that handles several cleanup tasks for you. It is worth running through its recommendations before you do anything manual, because it can automate Trash emptying, movie removal, and iCloud offloading.
Open the Storage Management window
On macOS Ventura and later, open System Settings, click General, then Storage, then scroll to the Recommendations section. On macOS Monterey and earlier, click the Apple menu, About This Mac, Storage, then Manage. You will see a set of recommendations with buttons to enable each one.
Enable Empty Trash Automatically
This option removes items that have been in the Trash for more than 30 days. Turn it on once and you never have to remember to empty the Trash again. It is one of the best set-and-forget settings for avoiding future warnings.
Turn on Optimize Storage
This removes watched Apple TV movies and keeps only recent email attachments locally. Combined with iCloud Drive, it can free tens of gigabytes without you touching a single file.
Review files in Reduce Clutter
Click Review Files under Reduce Clutter to see large files, downloads, and applications sorted by size. Delete anything you do not need directly from this view. It is a faster interface for cleanup than hunting through Finder manually.
Boot to Safe Mode or Recovery Mode when your Mac cannot start normally
When a startup disk is completely full, the Mac may stall on the boot screen, repeatedly restart, or show a flashing folder icon. In these cases you cannot reach Finder to delete files the normal way. Safe Mode and Recovery Mode give you tools to clean the disk from outside the normal boot environment.
Try Safe Mode first for an automatic cache flush
Safe Mode boots macOS with only essential extensions and deletes certain caches during startup, which alone can free a few gigabytes. On an Intel Mac, restart and hold the Shift key until the login window appears. On an Apple silicon Mac, shut down, then press and hold the power button until startup options appear, select your startup disk, hold Shift, and click Continue in Safe Mode. Log in and check whether the Mac responds normally.
Use Recovery Mode to delete files when the disk is completely full
If Safe Mode fails, boot to Recovery Mode. On Intel Macs, restart and hold Command-R. On Apple silicon Macs, shut down, then press and hold the power button until you see the startup options screen, then click Options and Continue. From the Recovery menu, open Terminal from the Utilities menu.
Delete files from Terminal in Recovery Mode
In Recovery Mode Terminal, your normal startup volume is not mounted at the root. First, identify your data volume by running diskutil list and looking for the volume named Data or the main APFS volume group. Mount it with diskutil apfs unlockVolume followed by the volume identifier. Then navigate with cd /Volumes/YourDataVolume and use commands like rm to remove specific large files, or du -sh * to find which folders are largest. Delete with care, because there is no Trash in Terminal.
Forum users on r/mac and Apple Support Communities report that this Recovery Mode approach is often the only way to recover a MacBook Pro that refuses to boot because the disk is full. The most reliable targets to delete from Terminal are old iOS backups in the MobileSync folder, large video files, and the contents of ~/Library/Caches.
Restart and verify
After deleting enough files to leave at least 10 GB free, restart normally. The Mac should boot into the regular desktop, at which point you can continue cleanup using the Finder-based steps earlier in this guide. Run a software update next, since a freed-up disk often unblocks a pending macOS update that was waiting for space.
Keep at least 20 GB free and run monthly maintenance to avoid the warning
Once your disk is healthy again, a short monthly routine keeps the warning from returning. Aim to maintain at least 20 GB of free space, which gives macOS room for virtual memory, system caches, and the next software update.
Run this monthly checklist
Empty the Trash, sort Downloads by size and delete anything older than 60 days, delete Time Machine local snapshots with tmutil, and run a Finder size search for files larger than 1 GB to catch new media before it piles up. This takes about 15 minutes and catches problems early.
Keep the automatic settings switched on
Leave Empty Trash Automatically and Optimize Storage enabled so macOS handles routine cleanup for you. Combine that with iCloud Drive and a reasonably lean set of installed apps, and the “Your disk is almost full” alert becomes a rare event instead of a monthly one.
FAQs
How to free up space on your startup disc on a Mac?
To free up space on your startup disc, start by emptying the Trash and clearing the Downloads folder, which often returns several gigabytes in minutes. Next, delete old iOS backups from Finder or ~/Library/Application Support/MobileSync/Backup, uninstall unused apps, and clear user caches in ~/Library/Caches. Removing Time Machine local snapshots with the tmutil command reclaims hidden space, and moving large media to an external drive or iCloud frees the most room of all.
How to free up space on Mac when disk is full?
When the disk is completely full, first empty the Trash and remove large files from Downloads to free a few gigabytes fast. If the Mac will not boot normally, start in Safe Mode to flush caches automatically, or boot to Recovery Mode and use Terminal to delete large files directly with rm after unlocking the data volume with diskutil. Aim for at least 10 to 20 GB of free space so macOS can boot and update normally.
Why is my startup disk full?
Your startup disk fills up from installed applications, personal documents and media, old iOS backups, accumulated cache and log files, and Time Machine local snapshots. The ‘System Data’ category often grows to 30 to 80 GB over a couple of years and is the most common source of mysterious space loss, especially when Time Machine snapshots are not thinned because the backup drive is disconnected.
What does it mean when my Mac says my disk is almost full?
The ‘Your disk is almost full’ warning means your Mac startup disk, usually named Macintosh HD, has less than about 15 percent of its total capacity remaining. macOS shows this alert because a full disk blocks software updates, slows the system by starving virtual memory, and can cause apps to crash or the Mac to fail to boot. Free up at least 20 GB to restore normal performance.
Wrapping up
Clearing a full Mac startup disk comes down to a predictable order: empty the Trash and Downloads, delete old iOS backups, uninstall unused apps, trim caches and logs, remove Time Machine snapshots, and move large media to external or cloud storage. Following that sequence lets you learn how to free up storage when your Mac startup disk is almost full without guessing, and most people reclaim 20 GB or more in the first hour.
Keep at least 20 GB free, leave Empty Trash Automatically and Optimize Storage switched on, and run the 15-minute monthly checklist so the warning does not come back. If your Mac ever refuses to boot, Safe Mode and Recovery Mode give you the tools to clean the disk from outside the normal environment and get back to a working system.