My new 64gb iPod touch only has 56.6gb of total storage. Does the operating system really use 7.4gb? My iPad uses less than half of that. P.S. I have deleted most of the free apps eg. GarageBand that came pre-loaded on my iPod. Thanks

It will not permanently consume that space. It's only required to update over the air. Once the update is complete, the space will be released.

If you don't want to bother deleting enough content to make room for it, update using iTunes and your computer. The space requirement does not apply when updating via iTunes.

That seems right. My 64 GB iPhone 6+ has 55,7 available.

Apps that can be deleted are not included in the available listing.

Does your iPad have 64 GB? The difference between the advertised capacity and the avaialbe is made up of both how much the operating system take and how GB is advertised and reported by the device. See:

How OS X and iOS report storage capacity - Apple Support