There are 5280 feet in a mile. Thus, if your stride is 18 inches (1.5 feet), then there are 3520 steps per mile (5280/1.5). If your stride is 2 feet, then there are 2640 steps in a mile (5280/2). Most peoples stride is longer when running when walking, so there are less steps per mile. Its a fairly personal thing that there is no easy answer to.
Measure your stride (Walk 10 steps, measure the distance and divide by 10 for more accuracy), convert the inches to feet by dividing by 12, so if you come up with a stride of 27 inches, that is 27/12=2.25, then divide 5280 by your answer, 5280/2.25=2347 (rounding up).
@cbrfan, to have 10000 steps equal 5 miles, the required pace length is about 2.64 ft. which is long for walking, but probably a decent running pace length.
Hope that helps