It’s 1 unit.
I could have chosen to start with a 10 unit sphere, it’s an arbitrary choice.
For some softwares, 1unit is 1mm for other its 1m, etc, There is no right or wrong. It only matters if you want to 3d print it.
You should expect to scale by 100/10 (no one should use inches though) when you use multiple softwares that don’t share the same convention, it’s common.
Yep that’s it.
Unit is sometimes confusing for users, see Enter numbers for scaling and sizing - #8 by Spud