How much of 1TB HDD need to be free?

[levmc]

I was thinking if there wasn't enough space in HDD, it could start to lag. How free space should you ideally have?

 

[Anonymous Freak]

In general, you should keep at least double the amount of RAM in your system empty. If you have a 1 TB drive, and 16 GB RAM, keep at bare minimum 32 GB free. If your system has an SSD, you should keep at least 10% free. If it's a spinning drive, you can go as low as 5% before you start really running in to performance issues. (macOS defragments hard drives automatically - if using an OS that doesn't, more is better.)

 

[Fishrrman]

You'll have to experiment.
The OS needs "room to breathe" by having space to write the VM swap and temp files.
Apps need space for temp files as well (at least some of them do).
I'd say 10-15gb for a "minimum".
If that slows things down too much, clear off more space.

 

[Quixotic3]

at least 15% remember that the OS is about 20Gb so if you are upgrading the system you need to count that space as well. I use a Samsung t5 for my photos and iTunes as they take the most room on my drive and I still get 400 read/write

 

[Thessman]

On A HDD ( and not a SSD) the ideal is to leave it at 50% full, if you fill it up more then the speed deteriorates rather quickly.