Simple guide to formated capacity:
FormattedSize = Size * .93
So
40 * .93 = 37.2
200 * .93 = 186
500 * .93 = 465
1000 * .93 = 930
2000 * .93 = 1860
As you can see, this rule is pretty close to fact.
When the 7tb drive is released, it will format to 6510gb.