Body Mass Index

Most kids can remember measuring their arms with a skin-fold pincher in gym class or making sure they stayed in the "healthy color" on the doctor’s weight chart at the annual physical. Both physicians and parents realize the importance of monitoring children’s growth to ensure healthy development. But once those children have matured and stopped growing and having that yearly check-up, how are they supposed to make sure they are living healthy lifestyles?

With 30 percent of Americans obese and nearly half overweight, we know that many adults are living unhealthily. However, many do not realize the serious health effects that accompany excess weight. The terms overweight and obese are used to identify ranges of weight that have shown an increase in the likelihood of certain diseases and health problems, such as cardiovascular disease, high blood-pressure, cholesterol, and diabetes.

To help avoid these conditions, health experts have designed a non-invasive procedure to measure healthy body compositions that can be easily completed by any individual.

What is body mass index?

Body mass index (BMI) is an indirect measurement of a person’s total body fat, calculated with a height-to-weight ratio. Recommended by doctors, the measurement has proven to be accurate when compared with actual body fat percentages and helpful in defining weight status. All that, and it's as easy as counting pounds and inches.

How is BMI measured?

Body mass index is calculated using the following equation:

BMI = (Weight in Pounds/(Height in Inches)^2) * 703

For example, a 5-foot-7 woman who weighs 150 pounds would divide 150 by 67^2 and then multiply that by 703. This woman’s body mass index is 23.49.

What does my BMI calculation mean?

A person’s BMI calculation does not mean anything until it is applied to the weight status levels established by health experts.

BMI of 18.5 or lower = underweight
18.5 – 24.9 = normal weight
25 – 29.9 = overweight
30 or higher = obese

In analyzing the above woman’s BMI, we find that she is at a normal weight for her height.

How does BMI vary from person to person?

Body mass index is measured and interpreted the same way for adult males and females. They have stopped growing and will maintain relatively the same height for the rest of their lives. Meanwhile, their weight will most likely fluctuate throughout adulthood. Body mass index measures the healthiness of those changing weight levels.

BMI measurements are not as accurate for serious athletes whose weights consist mostly of muscle mass and little body fat. Bodybuilders, for example, could be mistaken for being overweight when most of their mass is heavy muscle. Alternative body composition measurements, such as waist size, would provide more accurate statistics for such individuals. Conversely, most adults lose muscle mass as they age and could be falsely placed in a lower weight status level. In this case, more in-depth body fat composition tests would prove more accurate than weight.

Age-specific BMI for children

Since children are continuously growing and vary in body composition during different stages of their development, their body mass index must measure more than just their height and weight. Also, boys and girls’ bodies mature differently, so BMI calculations for children must be age and gender-specific.

Doctors plot children’s weights on gender-specific growth charts and use a percentile system to classify and compare their body mass index to norms for children of that age. This provides an accurate system of tracking body growth throughout development and assessing any health risks associated with abnormal development. The following weight status levels have been established:

Under 5^th percentile = underweight
5^th-85^th percentile = normal
85^th – 95^th percentile = at risk for being overweight
95^th percentile or higher = overweight

BMI tips

- Be sure to measure height and weight carefully
- Use an online calculator for exact calculations
- Pay attention to the weight status levels – if the results say overweight or obese, start making healthier life choices or speak with a doctor.