In rough order of how much space they return for the effort: thin local
Time Machine snapshots, delete old iOS device backups, empty
~/Library/Caches, clear developer caches if you write code,
empty the Trash including the per-app ones, and turn on Optimise Mac
Storage for Photos. That covers most Macs. Everything below is the detail,
including the part where the space you free does not match the size the
folder claimed.
01 Check this before anything else
Open Terminal and run df -h /. Note the available figure.
Then run:
tmutil listlocalsnapshots /
If that prints a list, macOS is storing point-in-time copies of your
volume on the same disk, taken several times a day. On most Macs this is
the biggest single block of reclaimable space, tens of gigabytes, and it
is invisible in Finder. To reclaim roughly 50 GB of it:
tmutil thinlocalsnapshots / 50000000000 4
Run df -h / again to see what actually changed. This is the
highest-yield thirty seconds available to you, and it is why the machine
can insist the disk is full while Finder shows free space. That
particular contradiction has its own guide:
disk full but space available.
02 Old device backups
If you have ever backed up an iPhone or iPad through Finder, those
backups are on this disk, in
~/Library/Application Support/MobileSync/Backup. They are
frequently over 100 GB, nothing tells you they exist, and Storage
settings files them under System Data where you cannot see them.
Manage them from Finder → your device → Manage Backups,
or just look in that folder. Keep one recent backup per device you still
own. Delete the rest, particularly the ones for phones you no longer have.
03 Caches and the Trash
Empty every Trash, not just the Finder one. Photos,
Mail, and Notes each keep a Recently Deleted bin that holds full-size
data for up to 30 days and does not appear in the Finder Trash.
Clear application caches. Quit the app, then delete
its subfolder from ~/Library/Caches. It rebuilds itself.
Browsers, Slack, Spotify, and Adobe apps are the usual heavyweights.
Downloads and Desktop. Sort by size in list view.
Installers, disk images, and old exports accumulate here and are
almost always safe to remove.
Restart. A reboot forces macOS to run cleanup it has
been deferring, so purgeable space often drops on its own afterwards.
04 Photos, iCloud, and the big libraries
A Photos library that has been running for years is genuinely large, and
deleting photos is not the answer. Turn on Optimise Mac Storage
in Photos settings and macOS keeps smaller versions locally while the
originals stay in iCloud. Same idea for iCloud Drive, in
System Settings → Apple Account → iCloud.
One caveat worth knowing: files stored only in iCloud leave behind a
placeholder, a dataless file. Finder and most disk tools report the
placeholder at the full size of the original, so a folder that costs you
almost nothing locally can look like 40 GB. If your storage maths
seems impossible, this is often why.
05 If you write code
Developer tooling is usually the largest thing on a developer's Mac, and
almost all of it regenerates. Xcode's DerivedData, iOS DeviceSupport
folders for every OS version you ever connected, simulator runtimes, and
archives together run to 100 GB or more on an active machine. Docker
images, npm caches, Homebrew downloads, and Gradle or Maven repositories
add more.
All of it is safe to clear, with the only cost being a slower next build.
The commands and what each folder is for are in our guide to
clearing Xcode and developer caches.
06 Why the numbers will not add up
At some point you will delete a folder Finder said was 87 GB and
free 12 GB. This is the single most confusing part of managing
storage on a modern Mac, and it is not a bug.
APFS uses clone-on-write. When a file is copied, the copy points at the
same blocks as the original until one of them changes. Both files report
their full length. Only one copy's worth of space is actually used.
Finder's Get Info, du, and most disk visualisers sum logical
file sizes, so they count those shared blocks once per file. Add hardlinks
and iCloud placeholders and the reported total can be wildly higher than
what is really there.
So "which folder is biggest" is the wrong question. The right one is
"which folder will give me the most back", and those are different lists.
The full explanation, with the syscalls, is in
Counting bytes on APFS.
07 When the easy wins run out
Once snapshots, caches, and backups are dealt with and the disk is still
tight, you are looking for real, unique data, and you need to see it
rather than guess. That means mapping the volume.
Delve draws every folder as a rectangle sized by the
space it genuinely occupies. Clones and hardlinks are counted once rather
than once per copy, and iCloud dataless files are marked, so the number
next to a folder is the number you get back by deleting it. Big
rectangles are the folders worth your attention, and you get from "the
disk is full" to "it is these two folders" in about fifteen seconds. A
1 TB volume scans in well under two minutes on a base M2.
It is native, it never sends your filesystem anywhere, and it is $4.99
once after a 14-day free trial. If you would rather pay nothing,
GrandPerspective is free and
open source and draws a treemap too, without the APFS accounting.
What is the fastest way to free up space on a Mac?
Thin local Time Machine snapshots with
tmutil thinlocalsnapshots / 50000000000 4. On most
Macs it is the largest single block of reclaimable space and takes
under a minute. After that, old iOS device backups and
~/Library/Caches.
How do I free up space without deleting anything I need?
Everything in the first three sections here regenerates: snapshots,
caches, and developer build folders all come back on their own.
Turning on Optimise Mac Storage for Photos and iCloud Drive frees
space without losing files at all.
Do Mac cleaner apps actually work?
They mostly delete ~/Library/Caches and empty the Trash, which you
can do yourself in a couple of minutes. They cannot clean System
Data as a unit because it is not a folder, only an uncategorised
remainder in Storage settings.
Why is my Mac still full after deleting files?
Two common reasons. Deleted files may still be held in local Time
Machine snapshots, and on APFS the folder you deleted may have
shared its blocks with files that still exist, so its reported size
was never space you could reclaim.
How much free space should a Mac have?
Aim for at least 10 to 15 percent of the volume free. Below that,
macOS has less room for swap and snapshot management, and the
system starts spending effort on reclaiming space instead of doing
what you asked.