Restore of database failed .bak file SQL Server 2008
You need to check the actual size of the database files which you can check by running

RESTORE FILELIST ONLY FROM &lt;backup_device&gt;   

This will give you information about the files contained in the backup and their sizes in bytes

You need the same space available on the server as the database file size, the backups can be compressed. 

Now you need to free up more space on c: on the server but I would recommend that you add drives to your server and that you would look at storage best practies