I have an iPad Air and I want to update this game that needs 1.4 GB. I only have 5 apps on my iPad and when I go to Settings to look at my storage it says I have used 11 GB. I added up the usage for all my apps and I counted only 3.3 GB. I don't know how to fix this, I've restarted my iPad but it didn't work. I don't know where the other 8 GB is coming from. I also have the same problem on my iPhone 4s.
First, you should update your iPad to the latest iOS system and then if it still takes up you much space, I guess maybe there is much junk files or "other" storage on your iPad Air. You should know what is the Other storage clearly firstly. There are just too many things that require physical storage. That's why Apple chose to lump a lot of things into the "Other" category. Also you can refer to this thread who has the similar situation with you. Hope it's helpful to you. https://www.reddit.com/r/iphone/comments/3elqfe/iphone_6_says_storage_almost_fullexcept_its_not/