Most people try to solve a full disk by opening Finder and dragging whatever looks big toward the Bin. That is how important files disappear. These guides work the other way around: measure first, decide second, remove third. This page sets up that habit and gives you the vocabulary the rest of the site assumes.
Open the storage screen
- Open System SettingsClick the Apple menu in the top-left corner and choose System Settings. On older machines the panel is named System Preferences; the path below is the same either way.
- Go to General, then StorageChoose General in the sidebar, then Storage. macOS may take a few seconds to calculate, and a small progress indicator shows while it scans the disk.
- Read the barThe coloured bar splits your drive into groups such as Documents, Photos, Mail, Messages, System Data and the space that remains. Segments are selectable, and each opens a short list of larger items in that group.
- Note the suggestionsApple offers one-tap ideas such as keeping files in iCloud or reviewing large items. Treat them as suggestions, not instructions, and read what each one does before you agree to it.
- Write down two numbersTotal capacity and the amount still available. Everything that follows can be measured against those two figures, so you will know whether your work actually helped.
Do not remove anything yet. The aim of this chapter is only to make the disk legible: to turn a vague worry into a set of named groups with sizes attached.
What the categories mean
Documents is everything in your home folder that is not otherwise classified: Desktop, project folders, exports and archives. Photos covers your Photos library and the media the system indexes for it. Mail and Messages count the attachments and chat media those two services keep on the drive. System Data is the broad remainder: caches, logs, indexes, device backups and local snapshots. It is the group people understand least and empty most carelessly, which is why it has a chapter of its own.
One honest note about the bar: the groups overlap slightly, and the numbers can shift while macOS recalculates. Treat them as a map, not a bank statement. The map is good enough to point you at the right neighbourhood.
Find the real size of any folder
Finder can measure folders, but the option is switched off to begin with. Open any Finder window, choose View > Show View Options, and tick Calculate all sizes. Within a few seconds the Size column stops showing dashes and starts reporting how much space each folder occupies. Click the top of the Size column to sort: your heaviest folder rises to the top. This one habit is the most useful skill on the whole site.
For a quick figure on a single item, select it, press Command+I for Get Info, and read the Size line. Get Info reports the logical size, while Finder's column can differ a little because of compression and cloning; both are close enough for a decision.
Keep a second copy before you remove the first. Before deleting anything you cannot recreate, make sure a duplicate exists on an external drive, in iCloud or with a backup. Removing an item is easy; replacing it is often impossible.
Three rules that keep you safe
- Remove copies, never originals. Export, upload or back the item up before you touch the last instance of it.
- Empty the Bin last. While an item sits in the Bin it costs nothing extra and can be restored in one click.
- Change one thing at a time, then re-check Storage. If the number did not move, nothing was really recovered.
A short glossary of terms
Four words recur in nearly every chapter. Learn them here and the later pages read cleanly.
| Term | What it means in practice |
|---|---|
| Library | A folder that macOS manages as a single unit, such as the Photos library. It holds your originals, previews and indexes together. |
| Snapshot | An hourly copy of changed files that Time Machine keeps on the internal drive, usually for about a day. |
| Cache | A copy of data kept to speed something up. Usually safe to clear, and usually rebuilt on its own. |
| Index | A catalogue that makes searching fast, such as Spotlight's index. It can be rebuilt if it grows too large. |
How to read a procedure
Every numbered procedure on this site follows the same shape: an explanation of what you are looking at, the steps in order, and a note on what is safe to remove. Where a step could destroy the only copy of something, a warning block appears. Read the warning before the step, not after it. When a chapter finishes, the Recheck habit applies: return to Storage, confirm the change, and then move on.
If a word here is unfamiliar, this page is the place to come back to. Bookmark it, and treat the map above as the ground floor of everything else on the site.