There are 5280 feet in a mile, and 12 inches in a foot, so there are 63,360 inches in a mile: so figure out what the stride length is for your machine (typically it is 15-18 inches) and plug it into the equation 63360 / X = how many strides to a mile.
But the point of the elliptical workout is raising your heart rate to a steady pace for 20 - 30 minutes, not how far you ran... although it does help the sense of accomplishment to know how far you have gone! Happy running!