Mac storage basics · Checking your storage
How much free space should I keep on my Mac?
Short answer: Keep roughly 10–15% of the drive free. macOS needs room for virtual memory, snapshots and especially system updates; running near full causes slowdowns and failed updates.
Leave a comfortable margin — roughly 10–15% of the drive, and never less than a few tens of gigabytes on a small drive. macOS needs room for virtual memory, caches, local snapshots and, above all, system updates, which unpack and need much more space than their download size.
The tighter you run, the more you'll see slowdowns, failed updates and apps that can't save. A percentage is a better guide than a fixed number: 25 GB free is plenty on some Macs and very tight on a 256 GB one.
Storage Studio warns based on how fast space is disappearing and how much is left, rather than a fixed threshold, and its Emergency Space screen is there when you're nearly out. See freeing up space.