Capacity of drives

Legacy Products My Cloud OS 3
1

I have 2x4TB drives installed and half full of data. Windows says that there are 4.70TB free space and WD My Cloud EX2 says that there are 5.25TB free space. Why the difference? Who should I trust?

2

WD is reporting Terabytes…
Windows is reporting Tebibytes.

http://en.wikipedia.org/wiki/Tebibyte