How to free up space on a Mac when it says your disk is almost full

The 'Your disk is almost full' warning is more than an annoyance. A Mac with very little free space gets slower, cannot install updates, and may refuse to save large files. A common rule of thumb is to keep at least 10 to 15 percent of the disk free. Here is a calm way to get there without deleting anything you will miss.

1. See what is actually filling your Mac

Open System Settings, choose General, then Storage. Give it a minute to finish calculating. You will see a bar split into categories such as Applications, Documents, Photos, Developer and System Data, with the size of each. Start with the biggest block. Clearing one large category beats tidying five small ones.

2. The quick wins (about ten minutes)

• Empty the Trash. Files in the Trash still use space until you empty it, so glance at what is in there first.
• Sort your Downloads folder by size. Old installers and disk images (.dmg files) are usually safe to remove once the app is installed.
• Review Messages and Mail attachments. The Storage settings can show how much they use and let you review the biggest ones.
• Look for old device backups. Old iPhone and iPad backups can take tens of gigabytes. In Storage settings, look for an iOS Files or backups entry.
• Read the recommendations at the top of Storage settings, such as storing files in iCloud or emptying the Trash automatically. Turn on only the ones that suit how you work.

3. Remove apps you never open

Apps are often the second-biggest block. In Storage settings, open the Applications list and sort by size. Anything large that you have not opened in months is a candidate. Dragging an app to the Trash removes the app itself, and our guide to uninstalling a Mac app completely explains what it leaves behind.

4. Find the large files hiding in plain sight

Screen recordings, old movies, virtual machine images and forgotten project folders are the usual culprits. We wrote a separate guide on finding and deleting large files on a Mac with three methods, including one built into Finder.

5. Understand System Data

System Data is a catch-all category. Part of it is caches and logs that are safe to clear. Part of it is things macOS needs to run. Read what System Data is and how to reduce it and how to clear cache on a Mac safely before you touch anything in the Library folder.

What not to delete

• Anything inside the System or Library folders that you do not recognise.
• The contents of your Photos library. Manage photos from inside the Photos app, never by opening the library in Finder.
• Files in iCloud Drive, until you have checked they are also stored online. Deleting a synced file removes it from every device.
• The insides of an app. Delete the whole app, not pieces of it.

Doing it faster with an app

You can do all of the above by hand. If you would rather not, a cleaner app can show it in one place. We make one, Speed Up My Mac, so keep that bias in mind. It draws what fills your disk by type, finds junk and leftovers with a plain reason and a risk level for each item, and asks you before anything moves. You choose the Bin, where you can put it back, or delete permanently. It does not use the network.

Keep it from filling up again

Space comes back slowly and goes fast. The easiest habit is a short monthly pass. Our 20-minute Mac clean-up is a routine you can repeat, and it takes less time than the first clean-up you are doing today.