I used to go to a website and calculate the partition size but I unfortunately do not have access to it anymore. So, it has to be manual. This trick worked like a charm when I tried to resize a partition that was factory partitioned. I believe it would work for other situations as well.
What I did was for my 150GB partition after seeing someone's post in superuser.com.
Since I want a 150GB partition, I calculated like the following.
(1024 x 150 ) + 4 = 153604
For every 1GB, it should be multiplied by 1024 and then 4MB should be added.
Mission accomplished finally. :)