I have created partition in RHEL 5.5.
Its showing total size of disk /dev/sda 586.7 GB.
after cration of partition

[root@localhost etc]# fdisk -l

Disk /dev/sda: 586.7 GB, 586783129600 bytes
255 heads, 63 sectors/track, 71338 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sda1 * 1 4589 36861111 83 Linux
/dev/sda2 4590 23790 154232032+ 83 Linux
/dev/sda3 23791 42990 154224000 83 Linux
/dev/sda4 42991 71338 227705310 5 Extended
/dev/sda5 42991 62190 154223968+ 83 Linux
/dev/sda6 62191 71338 73481278+ 83 Linux

[root@localhost etc]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 35G 2.3G 31G 7% /
tmpfs 2.0G 0 2.0G 0% /dev/shm
/dev/sda2 145G 188M 138G 1% /u01
/dev/sda3 145G 188M 138G 1% /u02
/dev/sda5 145G 188M 138G 1% /u03
/dev/sda6 69G 180M 66G 1% /u04
-----------------------------------------------------
Total 541 GB

Now my problem is where 45GB of sapce gone?
Even its not showing any free cylinder as well
any thing i did wrong while doing partition?

Divide your df figure by your fdisk figure and get .92. Tried this on a 250G disk of mine and got .96. As you know some space is used up for the file systems thingies; however the amount used up with your thing does look a bit excessive perhaps. Might have a look at it with anoter partitioning tool.

Looks like it's using 1000 and not 1024 like df. You can try to use the same.

I do remember someone linked this too once

read the consumer confusion part
http://en.wikipedia.org/wiki/Gigabyte