This is normal,have a read of this taken from another thread
Hard drive manufacturers are deceptive when they label their drives.
In the computer world, by any measurement, from any operating system, the correct way to calculate a GB as 1024^3 bytes (1024 is 2 to the 10th power, raised to the third power = 2^30) or 1,073,741,824 bytes.
Hard drive manufacturers, however, count a GB as 1000^3 (1000 to the third power) or 1,000,000,000. "Everybody does it" is their lame excuse. AFAIK, these may be the only humans in existence* who's mothers didn't ask them, "If your friends all walked off a cliff...?"
Anyway, if you do the math you'll see the difference is about 7% (1-(10^9/2^30)) which is almost exactly the difference you are seeing between your formatted size and what Western Digital printed on the size of the box.
Because the terms GB or gigabyte have been so hopelessly contorted by hard drive manufacturers, a standards body has come up with a new set of unambigious terms; Gibibyte abbreviated GiB are now being used instead. While a GB could be mean 10^9 or 2^30, a GiB always means exactly 2^30 or 1,073,741,824 bytes.