My iphone storage is 12 g not 16 why ?

12.1 is about right.

There will be discrepancies between the capacity reported by the operating system and the advertising figure because of confusion and inconsistencies related to rounding, units and other mathematical minutiae. See Wikipedia for more on this.

You can expect to lose something like 3GB to 4GB of a 16GB iPhone's storage space, for example, to mathematical inconsistencies, as well as the space taken up by the operating system and other non-deletable installs. Which? ran a test and found that Apple's smartphones are actually among the most frugal in using up storage with initial installs, although you may find it harder to prune iOS than you would with other systems.

While Which? found that a 16GB iPhone 5s offers 12.2GB of true capacity, and a 16GB iPhone 5c allows 12.6GB, we checked a 32GB iPhone and were told it had a capacity of 28.3GB. And our 128GB iPad Air has a true capacity of 114GB. In our table above we have used tested figures as a guide when estimating the true storage available in other devices.

The iPhone IOS as well as the builtin apps take space as well.

If you deleted everything (including IOS) from the phone you would have more storage, but you would not be able to use the phone. IOS is a part of what is stored on the phone.

Ive just asked the same question. My other handsets have been 16gb but ive got at least 13.5 gb. My new iPhone 6 is only 12.1!!!

Shocking

These other handsets, are they running IOS8?