Messages taking up space on Mac, and how to trim it.

Why Messages takes up so much space on Mac

With iMessage on your Mac, every conversation from your iPhone shows up there too, and so does everything in it: photos, videos, voice notes, and files. Messages keeps them all, because Keep Messages is set to Forever unless you change it. Years of group chats with video add up to tens of gigabytes.

The text of your conversations is small. The attachments are what's big. macOS guards this folder: on the Mac this page was written on, Terminal got “Operation not permitted” trying to list it, so measure it with Storage settings instead, which can see inside.

How to reclaim space from Messages

Keep messages for less time

1. Open Messages settings. In Messages, choose Messages › Settings, then click General.
2. Change Keep Messages. Pick 1 Year or 30 Days instead of Forever.
3. Let it run. Messages deletes conversations older than that, attachments included, and keeps doing it from then on.

This is the one that keeps working. It's also the bluntest: older messages are gone, text and all, and if Messages in iCloud is on, they're gone from your other devices too.

Delete the biggest attachments

1. Open Storage settings. Choose Apple menu › System Settings › General › Storage.
2. Open Messages. Click the info button next to Messages. You'll see attachments sorted by size, with the biggest videos at the top.
3. Delete what you don't need. Select attachments, click Delete, and confirm. The conversations stay; only those files go.

Store messages in iCloud

In Messages › Settings › iMessage, turn on Messages in iCloud. Or use the Store in iCloud recommendation at the top of Storage settings. Apple's description: all messages and attachments are stored in iCloud, and when storage space is needed, only recent attachments are kept on this Mac. You need enough iCloud storage to hold them all, and older attachments download again when you open them.

Is it safe to delete Messages attachments on Mac?

From Messages or Storage settings, yes; that's what they're for. A deleted attachment is gone from that conversation, so save any photo you want to keep to Photos or Finder first.

From Finder, no. Messages keeps a database, chat.db, of which file belongs to which message. Delete files from Attachments by hand and Messages still thinks they're there, so you get blank bubbles and a database that disagrees with the disk. It doesn't save you anything the two methods above don't.

Messages is one of several folders that grow on their own. See also iPhone backups, iCloud Drive, and everything else taking up space.