Speaking of apps ...

... (as we were),  there is as yet a small number of apps that come up on a search of the Apple App Store (part of iTunes) for 'quilting' - but that will change.

The Robert Kaufman Fabrics 'QuiltingCalc' app ('The Quilter's Little Helper') looks like a useful place to start.  It allows you to calculate fabric requirements for eight steps of the quilt-making process, including top fabric, batting, backing fabric and binding yardage, converting between imperial and metric measurements, and calculating setting triangle sizes. It is free for both iPhone and iPad from the App Store, so definitely worth a look if you use an honeod or iPad.  Preview here.