How would you know if you are overweight?

BMI is a crude guide: The bmi formula, english units, is (wt in lbs) x 703÷(ht in inches), see: http://en.Wikipedia.Org/wiki/body_mass_index. Optimal just below 20 to ~25 bmi range. However, if very muscular, bmi overestimates body fat. The bigger issue, healthwise, is body fat, which is driven by low-fat diet/foods (carb/sugar is rapidly converted to triglyceride fats, by liver ; stored). See nusi.Org, fatchance.Html.