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Your Mac is slow because its storage is almost full
A nearly full disk slows down the whole Mac, not only saving files. macOS needs free space to work. Here is how much to keep free, and the safe ways to get space back.
Why a full disk makes a Mac slow
When your apps need more memory than your Mac has, macOS moves some data from memory to the disk and back again. This is called swap. macOS also uses the disk for caches and for updates.
With little free space, macOS cannot do this work well. Apps freeze, the spinning wheel appears, and macOS can warn that your startup disk is almost full.
How much free space do you need?
Apple does not give one number. Sluggish warns when less than 20 GB is free. That is a simple rule of thumb: it leaves room for swap and caches. A macOS update can need more.
How to see what uses the space
Choose Apple menu › System Settings › General › Storage. The bar at the top shows how much each type of file uses. Click the ⓘ button next to a category to see its largest items.
Safe ways to free up space
- Use the recommendations in Storage settings. Apple can store your files and photos in iCloud, remove movies and TV shows that you already watched, and empty the Trash automatically (Apple Support).
- Empty the Trash. Files in the Trash still use space. In the Finder, choose Finder › Empty Trash.
- Clean out Downloads. Installers (.dmg files) and zip files that you already opened are often large.
- Remove large files that you do not need. In Storage settings, click the ⓘ button next to Documents. Sort by size and delete what you do not need.
- Delete apps that you never use. Drag them from the Applications folder to the Trash.
What not to do
- Do not delete files in the System or Library folders. macOS needs them.
- You do not need a cleaner app. macOS removes logs and caches that are safe to remove when space runs low.
- Do not worry if “System Data” looks large. It includes caches and local Time Machine snapshots, which macOS clears by itself when it needs the space.
Sluggish warns you before it gets bad
Sluggish shows your free space every time you click the gauge. When the disk is almost full, it says so in one line and opens Storage settings in one click. It never deletes a file.
Download SluggishYour first 10 checks are free, then $12 one time. macOS 14 or later, Apple silicon and Intel.