16GB is the raw size so once it's formatted you lose a bit of space right off the top. Next you have the OS itself which is what takes you to 11.8GB. Beyond that is any apps you have installed, photos, videos, etc, leaving you with what you see as available space.
My Galaxy S5 that I'm currently using is the same. 16GB raw, around 11.5GB actual space for me after the OS, and like 8GB left with all my apps and photos and whatnot. Just bringing this up as a reference so you know it isn't just an iOS thing. That being said, iOS apps are usually bigger than their Android counterparts, but they also tend to look better and often have more features.
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