160G raw disk will turn to 149G after formatted (1024 bits = 1kb, 1024 kb = 1Mb, and go on). And if some parts of the disk are bad and can not be used, chkdsk will mark them as unuseable and take them out of count. So total formatted size after a repair should be even less.
When a disk has some bad cylinders, the problem will get worse. I won't use this kind of disk for crucial storage.