remember:
GB = Gigabyte = 10003 bytes
GiB = Gibibyte = 10243 bytes
So, a BD-25 is
25,000,000,000 bytes / 1000 = 25,000,000 KB / 1000 = 25,000 MB / 1000 = 25GB = 25 x 10003
or
25,000,000,000 bytes / 1024 = 24,414,062 KiB / 1024 = 23,841 MiB / 1024 = 23.283GiB = 23.283 x 10243 (actually, 24,999,930,888 bytes and something)
so be careful to not mismatch GB and GiB - often I confuse myself, too!