Which capacity is my iphone 4s?

On my iphone, it says the capacity is 13.6 GB. However when I plug it in to my computer, when its connected to itunes it says it's ''iphone 16 GB''. How do I know which is it really?

Your iPhone is 16gb, the reason you're seeing 13.6gb is because some of the space is being taken by the firmware (iOS) so what you're seeing is usable storage not the full capacity of the device.

The actual sizes are always multiples of 2 (4, 8, 16, 32, 64, etc).

What you get to use is always less than that because of the space that the iPhone reserves for itself and the operating system.

It is 16GB but you only get 13.6GB to use. The rest is for iOS & other files.