The answer would depend upon the length of a person's step. However, an average person takes about 2000 steps to walk one mile. To learn how to do cardio walking correctly, see the page link, further...
Most US stair machine use 8 inches as the step height. This works out to 7920 steps. horizontal distance does NOT count for calculating a vertical mile. For a 170 # person doing this in one hour, you...