A Body Mass Index chart generally shows height in feet on the vertical axis and weight in pounds on the horizontal axis. BMI is calculated by dividing a person's weight in pounds by height in inches. A BMI of below 18.5 is considered underweight. BMI figures of 26 to 29 are considered overweight, while a BMI of 30 or greater is considered obese. These ranges are the same for all genders.
While BMI may be helpful for determining a person's healthy weight in some cases, on an individual basis it is often inaccurate because it does not factor in the difference between excess fat and muscle tissue. Muscle weighs significantly more than fat, therefore a lean, muscular person may have the same BMI figure as a person who is legitimately overweight. Men tend to have a larger amount of muscle tissue, and women carry more fat; therefore, men's BMI figures are often higher than women's, regardless of either person's overall health.