elliptical rpm vs mph ???

LisaStanley500

I just bought an app for my iphone to use while working out on the elliptical at home. lolo beat burn. Anyway, the idea behind it seems good enough, the "trainer" varies your workout & has you changting resistance & speed every few minutes. My question is this. "She" (trainer) keeps referring to speed as lets go 65 RPMs or 70 RPMs. My elliptical measures speed in MPH. How do I convert RPMs to MPHs? Just want to make sure I'm on track with the program. Also MAJOR descrepancy with calories burned. MFP says 363, my HRM says 587 & the app says 284. All the "helpful" technology is really ticking me off!! Please help.