25,025,314,816 bytes = 24,438,784 KB = 23,866 MB = 23.31 GB
That's the *best case* senario.
If the disc is formatted with what's known as 'spare areas' for error correction etc (part of the blu-ray standard), that size will be smaller still.
Thanks for your answer. Seems I got:
Looks like there's still a whole 1G missing. And I know about the 'spare area'. I just thought it was only ~26MB in size? I forgot about the 1024 != 1000 thingy, so that at least accounts for something.
EDIT: The BD-RE that came with the player is the one I'm talking about. Could just be that this is an el-cheapo model.