One of the lovely gals who works for me at the shop is an avid beader.
She told me about this little app for your phone or iPad called iBead. It gives a bead size guide, a bead calculator , a wire guide along with a little ruler and a seed bead guide. You can preview it on iTunes and the cost is $.99. I have used the little ruler as well as the size guides on numerous occasions when hunting for embellishments needs, so I thought other stitchers might find it useful as well.
Here is the link to the iTunes preview: