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Child BMI: Body Mass Index Calculator for Children

  • Synopsis: Published: 2010-12-27 (Revised/Updated 2017-06-26) - Calculate the BMI measurement of your child or children using our online Body Mass Index calculator for children aged 1 to 20 years. For further information pertaining to this article contact: Ian Langtree at Disabled World.
Body Mass Index (BMI)

The body mass index (BMI), or Quetelet index, is defined as a value derived from the mass (weight) and height of an individual. The BMI is defined as the body mass divided by the square of the body height, and is universally expressed in units of kg/m2, resulting from weight in kilograms and height in meters. If pounds and inches are used, a conversion factor of 703 (kg/m2)/(lb/in2) must be applied. When the term BMI is used informally, the units are usually omitted. A high BMI can be an indicator of high body fatness. BMI can be used as a screening tool but is not diagnostic of the body fatness or health of an individual.

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Quote: "It is important to have your doctor perform regular BMI measurements for your child so the doctor can discuss the results with you."

So what exactly is Body Mass Index (BMI)? BMI is a calculation that uses height and weight measurements to calculate how much body fat a person has. Doctors often use a BMI calculation to determine if a child's weight is appropriate for their height and age.


According to the CDC National Center for Health Statistics BMI, height, and weight percentiles show how your child compares to other children. For example, if you are 40th percentile in height, that means that you are taller than 40 out of 100 typical children of the same age and sex. If you are 70th percentile in weight that means your child is heavier than 70 out of 100 kids.

The Child BMI calculator below determines if your child is at a healthy weight for their age (up to 20 years of age), simply enter the required information and calculate their BMI level.

You can also check your child's height to weight ratio - Height to Weight Chart for Children.

NOTE: For Adult male and female BMI measurements you will need to enter your information into our Body Mass Index Calculator for grownups. In addition you may wish to try our Height to Weight Ratio Chart to measure an average adult's height/weight ratio.

Child Body Mass Index Calculator
Enter the following data
Gender of the child
Age of the child years
BMI (kg per meter square)
BMI percentile
BMI as a multiple of the mean BMI
Automatic recalculation

NOTE: It is important to have your doctor perform regular BMI measurements for your child so the doctor can discuss the results with you.

BMI is calculated the same way for both adults and children. The calculation is based on the following formulas:

Measurement UnitsFormula and Calculation
Kilograms and meters (or centimeters)Formula: weight (kg) / [height (m)]2

With the metric system, the formula for BMI is weight in kilograms divided by height in meters squared. Since height is commonly measured in centimeters, divide height in centimeters by 100 to obtain height in meters.

Example: Weight = 68 kg, Height = 165 cm (1.65 m)
Calculation: 68 A- (1.65)2 = 24.98

Pounds and inchesFormula: weight (lb) / [height (in)]2 x 703

Calculate BMI by dividing weight in pounds (lbs) by height in inches (in) squared and multiplying by a conversion factor of 703.

Example: Weight = 150 lbs, Height = 5'5" (65")
Calculation: [150 A- (65)2] x 703 = 24.96

Disabled World also provides a number of informative articles and information relating to Childhood Obesity

Awareness: Child Obesity Awareness Information

Yellow awareness ribbonThe color of the obesity, including childhood obesity, awareness ribbon is yellow.

The month of September is National Childhood Obesity Awareness Month - President Barack Obama proclaimed September as National Childhood Obesity Awareness Month, encouraging Americans to help our youth lead more physically active lifestyles and make healthier food choices. Childhood obesity has increased more than fourfold among those ages 6 to 11. More than 23 million children and teenagers in the United States ages 2 to 19 are obese or overweight.

Facts: BMI

  • BMI can be used for population assessment of overweight and obesity. BMI is generally regarded as a satisfactory tool for measuring whether sedentary individuals are underweight, overweight or obese with various exceptions, such as: athletes, children, the elderly, and the infirm.
  • BMI is proportional to mass and inversely proportional to the square of the height. So, if all body dimensions double, and mass scales naturally with the cube of the height, then BMI doubles instead of remaining the same. This results in taller people having a reported BMI that is uncharacteristically high, compared to their actual body fat levels.
  • BMI is interpreted differently for children and teens, even though it is calculated using the same formula as adult BMI. Children and teen BMI needs to be age and sex-specific because the amount of body fat changes with age and the amount of body fat differs between girls and boys.
  • Obesity among 2- to 19-year-olds is defined as a BMI at or above the 95th percentile of children of the same age and sex in this 1963 to 1994 reference population. For example, a 10-year-old boy of average height (56 inches) who weighs 102 pounds would have a BMI of 22.9 kg/m2. This would place the boy in the 95th percentile for BMI - meaning that his BMI is greater than that of 95% of similarly aged boys in this reference population - and he would be considered to have obesity.
  • A BMI that is less than the 5th percentile is considered underweight and above the 95th percentile is considered obese. Children with a BMI between the 85th and 95th percentile are considered to be overweight.
  • Recent studies in Britain have indicated that females between the ages 12 and 16 have a higher BMI than males of the same age by 1.0 kg/m2 on average.
  • The prevalence of adult BMI greater than or equal to 30 kg/m2 (obese status) has greatly increased since the 1970s. Recently, however, this trend has leveled off, expect for older women. Obesity has continued to increase in adult women who are age 60 years and older.
  • BMI generally overestimates adiposity on those with more lean body mass (e.g., athletes) and underestimates excess adiposity on those with less lean body mass.

Related Information:

  1. Calculating Weight in Children with Eating Disorders - Experts Urge BMI Method - University of Chicago Medical Center - (2012-01-04)
  2. Underdiagnosis of Obesity when Using Body Mass Index (BMI) - American Association of Clinical Endocrinologists - (2010-03-29)
  3. Body Mass Index and Thrombogenic Factors in Newly Menopausal Women - American Physiological Society - (2010-08-28)

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