Maybe you should try the seagate tools to do the format. My rough calculation shows that you should have ~1460000 MB available. There will be some reserved space for bad clusters, but..... Maybe you should also run Seagate's diag tools first as a precaution.
Actually, 1,500,000,000,000 bytes is equal to:
1,464,843,750 kilobytes (original/1024)
1,430,511.47 megabytes (original/(1024^2))
1,396.98386 gigabytes (original/(1024^3)
1.36424205 terabytes (original/(1024^4))
(this is how the OS measures it)
Note that as you get to larger and larger measurements, the error actually seems to grow. Your drive is fine.