Best Practices - how much free space on main hard drive?

Title says it all. Everyone and lots of places say not to have your main hard drive too full but I can’t seem to find a percentage or absolute size that is considered optimal or best practice. I know I’m pushing my own system nearly to breaking point, 1 TB drive that only has 40GB free but wondering what I need to get to. Trying hard to figure out what I don’t need so far it’s mostly apps I never use like Garage Band, iWeb, server app now I’ve got the Synology doing server duties etc.

Rule of thumb I heard (and have relied on) for decades is to keep 15-20% free. Good discussion thread here:

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Ever since Mojave: I think let the OS manage it, and ignore anything else. I’ve found the OS very capable of managing disk space. BUT it is related to an icloud setup. Which I’m not sure you also have?

I try to keep free space to 20%. This gives me headroom for housekeeping, etc. It was more important in early days on Windows than today.

If you aren’t having any issues, then 40GB is fine. I think the 10-20% rules of thumb of old are outdated with 1TB drives (my opinion, no data or refs).

Backup software (and others) that need scratch space will complain if they can’t do their duty.

As far as managing your space, DaisyDisk is good for visualizing space, Gemini is good for finding duplicates, and CleanMyMac for finding old iOS backups, caches, etc. (although I usually don’t bother with deleting cache files unless space is really tight). CleanMyMac will also let you know apps that you haven’t used in awhile.

If you’re using it, I recently deleted iMazing because it blew up with massive iOS backups.

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I’m not on Mojave yet, and I do not use iCloud for anything but Safari bookmarks, so everything is on my machine. Doing some housecleaning getting rid of old installs for older revs of software I was able to get things to 175 GB available. I used to keep all old installs because our Internet access was sometimes iffy. However, now we have multiple redundant high speed Internet links so I am more comfortable with trashing all the old install software.

Where did you find those? I do use iMazing a lot and need it for some stuff.

I don’t recall.
There’s a setting in the prefs that should let you know:

I’ve typically taken the approach to move such files to external USB drives and/or external hard drives. In the “good old days”, they lived on ZIP drives (and before that on floppies). I also archive folders of “completed projects” to an external hard drive on a routine (yearly basis).

I believe that you can remove MAS apps and, should you need them later, just re-install “from the MAS cloud”.


Is this a SSD? If so you should have around 15% free for “garbage collection” and the more free space you have the better the drive can preform wear leveling. A spinning drive can probably do with less, and if it were me I’d aim for 50-100GB just to make sure I don’t run into issues.

Old spinning drive. I’m trying to offload some more but managed to get just about 100GB free.

in addition to find duplicates and help delete stuff, the following apps have been helpful to me: App Cleaner, DaisyDisk, Gemini 2, and Forklift. There might be more, if so people let me know if I missed any.