I used to dual-boot Windows and Ubuntu on my previous laptop and everything worked just fine. I got a new 500gb HP Laptop and after installing Ubuntu, I realized that about 100gb was missing. Ubuntu is allocated to 114gb and Windows is allocated to 256gb. I have no idea where the other space went to and I want to know if it can be recovered.
Use Gparted, you can install it by typing
sudo apt-get install gparted
It has got a GUI so it is pretty easy to use, it is a package to display all your mounted drives with their partitions and sizes included.
Here is the official website with help, for your information it would be enough to install it and check the differences, if you would like to manage your partitions however, you will have to mount it live and do it from your live medium (flash disk e.g.).