Body Mass Index

The body mass index is a gauge for the amount of body fat in an individual. It is a number derived by multiplying one’s weight in pounds by 703, then divided by the height in inches two times. The same formula applies to both males and females. For example, if the adolescent’s height is 68 inches and weight is 140 pounds, then the formula would be applied as follows:

140 x 703 = 98420

98420/68 = 1447.35

1447.35/68 = 21.28

In this case the BMI would be rounded down to 21.

Why bother with the BMI? Tables used by insurance companies seek to determine those weights that are based on lowest mortality for men and women from ages twenty-five to fifty-nine years. And these weights are based on height and body frame. The unique characteristics of adolescents including their younger age are not taken into consideration in these tables. Furthermore, the insurance company tables have been criticized for representing those individuals who do not have chronic illness, selecting a non random sample from the population to derive the tables, arbitrarily lumping people into three body frames and finally, about twenty percent of the individuals used to develop the tables were not actually measured. This would lead to women tending to underreport their weight and men to over reporting their height.

The BMI correlates well with other estimates of fatness. The BMI does change dramatically with age during childhood and adolescence. The average ten year old has a BMI of about 16.8, while the average sixteen year old has a BMI of approximately 20.5. Federal guidelines define overweight as a BMI of more than 24 to 30, obesity as 30 or more. Extreme obesity is a BMI value of 40 or more. The “normal” range is 18.0 to 24.0 and underweight is classified as a BMI under 18.0. The BMI may not be as well suited for the adolescent athlete who has dense muscle mass and therefore may have a slightly higher BMI. Also, for teens who are still growing, the BMI may not be as reliable as a measurement tool. During puberty, changes in body proportions, bone mass and the ratio of lean to fat tissue change at different times for each adolescent. As a result of these growth issues, the BMI may be a better measurement when the teen has completed his or her growth.

Studies have demonstrated that the average BMI increases with age during adolescence and it tends to be slightly higher for females compared to males. The average BMI for sixteen-year-old Asian boys (18.9) is lower than that of African American boys (21.9). The average BMI for Hispanic sixteen-year-old males is 22.3 and for white males it is 22.1. For sixteen-year-old Asian females the average BMI is 21.5 compared to 22.6 for African American females 22.4 in Hispanics and 21.9 in Caucasian sixteen year olds.

The table below has calculated BMI values based on height and weight. It should be used only as a gauge since BMI vales in adolescents may not be as reliable as those in adults.

Body Mass Index Table


Height (inches)
	60	61	62	63	64	65	66	67	68	69	70	71	72	73	74	75	76
Weight (lbs)
130	25	25	24	23	22	22	21	20	20	19	19	18	18	17	17	16	16
135	26	26	25	24	23	22	22	21	21	20	19	19	18	18	17	17	16
140	27	26	26	25	24	23	23	22	21	21	20	20	19	18	18	17	17
145	28	27	27	26	25	24	23	23	22	21	21	20	20	19	19	18	18
150	29	28	27	27	26	25	24	23	23	22	22	21	20	20	19	19	18
155	30	29	28	27	27	26	25	24	24	23	22	22	21	20	20	19	19
160	31	30	29	28	27	27	26	25	24	24	23	22	22	21	21	20	19
165	32	31	30	29	28	27	27	26	25	24	24	23	22	22	21	21	20
170	33	32	31	30	29	28	27	27	26	25	24	24	23	22	22	21	21
175	34	33	32	31	30	29	28	27	27	26	25	24	24	23	22	22	21
180	35	34	33	32	31	30	29	28	27	27	26	25	24	24	23	22	22
185	36	35	34	33	32	31	30	29	28	27	27	26	25	24	24	23	23
190	37	36	35	34	33	32	31	30	29	28	27	26	26	25	24	24	23
195	38	37	36	35	33	32	31	31	30	29	28	27	26	25	25	24	24
200	39	38	37	35	34	33	32	31	30	30	29	28	27	26	26	25	24
205	40	39	37	36	35	34	33	32	31	30	29	29	28	27	26	26	25
210	41	40	38	37	36	35	34	33	32	31	30	29	28	28	27	26	26

And finally, taking all of the BMI values for seventeen-year-old boys, the average boy’s BMI is 21.8. For seventeen-year-old girls it is 21.2. According to insurance company data, for adults the average BMI for men is 22.4 and for women it is 22.5. Health risks increase as the individual’s BMI increases over 25.