Feb 5, - BMI is a number based on your weight and height. BMI is used to broadly define different weight groups in adults 20 years old or older. To use the table below, find your height on the left side of the chart, then go across to. Do you know what your ideal body weight is for a person of your height, To identify your frame size use a measuring tape and the height chart below. . a body mass index lower than 92% of all adult American women do, and would take an.