Because officially 1GB = 1024MB, but companies advertise and sell 1GB as 1000MB
16 GB iPhone = 16000000000 bytes = 14,89 GB
8,01 GB in use + 3,81 GB available = 11,82 GB total
The gap in between the 14,89 GB and 11,82 GB is most likely used for iOS, system files, etc.
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I also have a 16GB iPhone (5S) and have the following:
Used: 9,74 GB
Available: 2,23 GB
(Total would be: 11,97 GB)
