[danpalmer]

This would seem to be correct but doesn't take into account different hardware specs.

For a start, the larger the disk, the more is used for formatting and is lost due to the difference in how manufacturers specify sizes, so you can't just add/subtract storage amounts, you need to scale.

Also, different combinations of processor, cellular modem, etc, will require different parts of the operating system, and Apple differentiates between these in the distributions it provides. It's not a massive difference, but it is something.

Finally, on Mac OS, the operating system reserves some space for a memory dump if the device loses power so that it can resume where it left off. This means if you have 8GB of RAM, you will always have 8GB of disk space reserved (search for sleepimage). I don't know for sure, but iOS may do something similar.

[username3]

I agree with this. Also, if they calculate space in GiB instead of GB, we should add/subtract 14.9 and 29.8.