Space hogging files and folders

How can i find the biggest files and folders in /(root) file systems?

sudo du / 2>/dev/null | sort -rn | head
sudo du -a / 2>/dev/null | sort -rn | head

Thanks,

When running the following command:

du /var/ 2>/dev/null | sort -rn | head

I am getting the output:

41432328        /var/
19771516        /var/lib
15910316        /var/spool
15910188        /var/spool/mail
15796124        /var/lib/enswitch
5772612 /var/lib/enswitch/mailboxes
5725264 /var/log
5262072 /var/lib/enswitch/recordings
5211044 /var/lib/enswitch/recordings/sip
4639680 /var/lib/enswitch/backups

But when i am running the command:

du -h /var/ 2>/dev/null | sort -rn | head

I am getting the output:

1020K   /var/lib/enswitch/recordings/sip/989/940
1020K   /var/lib/enswitch/recordings/sip/934/177
1020K   /var/lib/enswitch/recordings/sip/896
1020K   /var/lib/enswitch/recordings/sip/828/262
1020K   /var/lib/enswitch/recordings/sip/574
1020K   /var/lib/enswitch/recordings/sip/564/910
1020K   /var/lib/enswitch/recordings/sip/540/758
1020K   /var/lib/enswitch/recordings/sip/438/264
1020K   /var/lib/enswitch/recordings/sip/425/287
1020K   /var/lib/enswitch/recordings/sip/301/566

I think i should have got the earlier output with the sizes in human readable form. But the output seems to be different. What is the reason?
Thanks in advance

"human readable" is a misnomer; it is really "abbreviated".

Since you are sorting abbreviations, not numbers, your results reflect that. 1030K is numerically larger than 1020M.