How do I know how much space I have used or left on my iPad? I have downloaded a lot of apps as well as music. I don't have a cellular plan and thus far don't need one. We're getting ready to buy another iPad and are not sure if the 16 gb will be sufficient. Will basically be used for apps, email, movies etc. Thanks!

Go to Settings/General/About

There you will see how much you have left under Available