There are 2 ways to convert from KB to say MB or GB. There's a binary conversion and a decimal conversion. The official SI standard dictates that K,M and G are multiples of 1000. This is also the standard harddisk manufactures use. Your computer however uses binary conversion (1024 or 2^10).

So binary conversion is:

1 GByte
1024 MByte
1048576 KByte
1073741824 Bytes

Decimal conversion (SI standard):

1 GByte
1000 MByte
1000000 KByte
1000000000 Bytes