Windows 8 comes with plenty of built-in useful apps like Mail, News, Weather and so on.
Here is how to find out how much space each of this installed app (and other newly installed apps from the Windows 8 store) are using :
1. From either the Start screen or Desktop, point the mouse cursor to top right or bottom right corner (or use Windows key+C). This will display a column of five icons and is called the Charms bar.
Select “Settings” from the Charms bar and click on “Change PC settings”.
2. From the “General” category, under the “Available storage”, select “View app sizes” .
3. This will display a list of all the installed Windows 8 apps along with the disk space being used by each of them.