13．During the teenage years，hormonal （荷尔蒙的） changes lead to physical changes like rapid muscle growth，burst in height，and weight gain in both boys and girls．Take a look at the information and height and weight charts（图表） for teens presented in this article if the question"How much should I weigh for my age and height"is bothering you．
Average Height and Weight Charts for Teens
Faster growth in kids usually can be noticed at age 8．Genetic factors also affect the physical growth of a child．So，it is perfectly normal for two kids of the same age to have different weights and heights．The following figures should be used as guidelines only．
| For Boys | For Girls |
| Age | Height | Weight | Height | Weight |
| in years | in inches | in pounds | in inches | in pounds |
| 12-13 | 58-62 | 85-100 | 60-63 | 95-105 |
| 14-15 | 63-66 | 105-125 | 63-64 | 105-115 |
| 16-17 | 67-70 | 130-150 | 64 | 115-120 |
| 18-20 | 68-70 | 150-160 | 64 | 125-130 |
Ideal Body Fat Percentage
Fit men have 14%-17% body fat．
Fit women have 21%-24% body fat．
Male athletes have 6%-13% body fat．
Female athletes have 14%-20% body fat．
The ideal body fat percentage varies mainly according to age，sex and the physical activity of the in-dividual．But it is a fact that some female athletes have body fat as low as 10% and some male athletes had lower than 4% body fat．So，it can be observed that other than the above mentioned factors，genetic factors also influence the body-fat ratio．
Body Mass Index （BMI）
You may use the following formula to calculate your BMI：
As per SI Units （国际单位）：BMI=mass （kg）/[height （meters）]
2Imperial （英制的） Units 1：BMI=mass （Ib．） x703/[height （in．）]
2Imperial Units 2：BMI=mass （Ib．） x 4.88/[height （ft）]
2Following conclusions can be derived from （得到） calculating the BMI：
| BMI Calculated | Conclusion |
| BMI 18.5～25 | Normal or ideal weight |
| BMI＞25 | Overweight |
| BMI＜18.5 | Underweight |
| BMI＜17.5 | Extremely underweight |
| BMI=30 or BMI＞30 | Obese（病态肥胖的） |
| BMI=40 or BMI＞40 | Extremely obese |
25．According to the Average Height and Weight Charts for Teens，C．
A．girls keep on growing taller during the teenage years
B．girls grow faster at the end of teenager years than boys
C．girls grow faster at the beginning of teenager years than boys
D．boys'average weight is always heavier than girls'during the teenage years
26．Which of the following statements about ideal body fat percentage is RIGHT？D
A．Fit men have higher body fat percentage than fit women．
B．Male athletes have higher body fat percentage than fit men．
C．Female athletes have lower body fat percentage than male athletes．
D．Male athletes have much lower body fat percentage than female athletes．
27．After calculating the BMI，you can reach the conclusion whetherA．
A．your weight is normal
B．your hormone level is normal
C．your height is right for your age
D．your body fat percentage is ideal
28．If a boy is 1.5 meters in height and weighs 68 kilograms，then he isB．
A．normal B．obese
C．extremely obese D．underweight．
