dvd sizes in k3b

I purchased a few 4.7 dvd rw's. When I format these disks under k3b, it gives the capacity as being 4.4 and I can't see an option to alter the format size. Am I missunderstanding something here? I remember some years ago, disk manufactures were sometimes using 1000k bytes as 1 meg etc and the answer was to multiply by 1.024, but this still doesn't give 4.7 gig. Peter C