iPhone storage too far from its actual total amount?

It appears that the storage space on my iPhone4S is not adding up to 16GB. I know 16GB is just the theoretical storage space, but currently, the total space seems too far away. Here's a screenshot of the storage status of my phone:

As you can see, 1.8 + 11.6 = 13.4GB. Where did the other 2GB go? Is this normal? Or are there residual files left on my iPhone that can't be cleaned up properly? I'm running out of space and so this means a lot to me.

Solution 1:

I'd say that's normal, my own 16GB iPhone 5 is adding up to 13.3 GB of available space. I would assume that the other space would be taken up by iOS itself, with system files, libraries etc. Also, as Kent mentions, the actual space is not 16GB to begin with.

Solution 2:

Keep in mind that you don't start with 16GB, but 16 x (1,000 x 1,000 x 1,000) ÷ (1024 x 1024 x 1024), or roughly 14.9 GB. So, the OS itself is only using up around 1.5GB.