An SD card, like the hard drive in your computer, needs room to operate. When it says "16 Gig", you will never get 16 gigs of actual recording space, but if you look at your machine, or put it into a computer, it will tell you how much space is available. I usually use 16 gig cards myself, and at 42/44.1, have no problem with a 2 day festival. I would suggest putting your card into your computer if you need to know your actual available space...of using a larger card to be safe.