Body Mass Index: Best Indicator of Body Fat

BMI is Calculated Using A Simple Formula

Curious to know how your child fares for his/her age? Kids or teens cannot be categorized as “overweight” without tracking their body mass index (BMI). Growing kids need to gain weight and outgrow their clothing size. The best measure to gauge whether your child is healthy or not is to measure and maintain records of his/her BMI. This is what your pediatrician does too for your child’s growth chart.

Since early times pediatricians have been using height and growth measurements to compare the growth of your child with other children in the same age group. Nowadays, they use a tool called BMI, which estimates body fat depending on your child’s height and weight. Although BMI does not measure body fat, it indicates whether a person has excess fat and if the person’s risk factor for any disease is multi-fold. This is the most simple and cheap method to calculate your health quotient. All you need to calculate a person’s BMI are his/her weight, height and a simple calculator or an online tool.

How to Calculate your BMI?
BMI calculations are easy. Just use your calculator to derive BMI values using either of the two basic BMI formulas depending on your choice. After calculating the BMI, round it off to the nearest whole number.

• Formula 1: BMI = Weight (kilograms) / Height (centimeters) / Height (centimeters) x 10,000
• Formula 2: BMI = Weight (pounds) / Height (inches) / Height (inches) x 703
  
  

Let's calculate BMI for a boy named John. If John weighs 59 kilograms(129 pounds) and is 160 centimeters (63 inches) tall, his BMI is 23.

•  Formula 1: BMI =59 / 160 / 160 x 10,000 = 23
•  Formula 2: BMI = 129 / 63 / 63 x 703 = 23
  

BMI Classifications for Kids
While BMI alone is enough to categorize adults into different weight categories (underweight, normal, overweight or obese), the same is not feasible for children as their body fatness changes as they grow. Further, girls and boys have different body fatness measures and we are forced to use gender-specific criteria to evaluate BMI in kids.

We use BMI-for-age-percentile growth charts to calculate BMI for boys and girls (aged between 2 and 20). In the graph, ages are plotted along the y axis and BMI values are plotted along the x axis and curves are drawn for different BMI percentiles. On the growth chart, you plot (mark) the point on the graph where your child’s age and BMI meet, and then you mark the BMI percentile curve on which the point lands on or the curves on either side of this point. The percentile values are just like your mark results indicating whether the BMI is in a healthy range or not just as your marks indicate whether you have passed or failed.
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Now, how do we classify BMI percentile? Medical experts have derived these categories based on pediatric body fat research:

Growth Chart for Boys

BMI	Category
​Less than 5th percentile	​Underweight
​Between 5th and 84th percentile	​Healthy Weight
​Between 85th and 94th percentile	Overweight
​Greater than 95th percentile	Obese

While these values and classifications are for our reference, never use terms such as “overweight” or “obese” in front of your children. Rather stick to the basics of discussing about a healthy weight and a nutritious diet.

The Potential Use of a Growth Chart
One BMI calculation is not enough to classify your child’s weight category. Kids grow rapidly and their heights and weights change as they grow up. Therefore, pediatricians maintain a growth chart to track BMI over time. Also, athletic or muscular teens/children may have higher BMI values because of extra muscle mass. Don’t mistake it to be body fat instead.

Finally, BMI is a tool for screening weight problems and cannot be used to make a final diagnosis. It is better to meet a health care professional or a registered dietitian nutritionist at www.firsteatright.com if you feel that your BMI values are slightly on the upper side. They are the right people to suggest healthy diet plans to lose weight, if needed.