You should look for a time piece as opposed to how many steps you take. Anything after your aerobic threshold (when you can't talk while your jogging) is good for your heart, and anything from 20-50 minutes will do. Anything over that will start causing exhaustion. Or even better, don't jog and do 50m sprints. Do three sets of 10 X 50 metres. After every 50 metres, take a break according to how long you took to run that 50 metres. I.e run 50 metres 15 seconds, rest for 15 seconds. So the point is the more tired you become, the more rest you have. I find sprinting to get fitness is better, in order for jogging to be of any real benefit, you need to be in pain for an extended period of time.
P.S run on grass, or it'll wreck the cartilage between your needs.