From GI News
According to a 2008 study on walking and maintaining a healthy weight, men ages 18–50 should take 12,000 steps a day. For men 50 and up, you'll need 11,000 steps a day. Women ages 18–40 need to take 12,000 steps a day, whereas women ages 40–50 should take 11,000 steps a day. Women in their 50s should take 10,000 steps a day, and women 60 and older should take 8000 steps a day. A rough estimate of how far you need to walk: depending on your stride, the average person takes about 1000 steps for every 0.8 kilometer (or about a half mile). To walk 11,000 steps is roughly equivalent to 8.8 km (5.5 miles).