Paediatric BMI Calculator
Use this calculator to determine a child's Body Mass Index (BMI). Please note that for children and adolescents, BMI is interpreted differently than for adults, using age- and sex-specific growth charts. This calculator provides the raw BMI value and a general classification, but a healthcare professional should always be consulted for accurate interpretation and health advice.
Understanding Paediatric BMI
Body Mass Index (BMI) is a screening tool used to estimate body fat based on a person's weight and height. While it's a straightforward calculation for adults, its interpretation for children and adolescents (ages 2 to 20 years) is more nuanced and critical for assessing their growth and health.
Why Paediatric BMI is Different
Unlike adults, children are still growing and developing. Their body composition changes significantly with age and varies between sexes. Therefore, a single BMI cutoff for "healthy weight" doesn't apply to all children. Instead, paediatric BMI is interpreted using age- and sex-specific growth charts, typically presented as percentiles.
- Age: A child's BMI naturally changes as they grow. What might be a healthy BMI for a 5-year-old is different from a 15-year-old.
- Sex: Boys and girls have different growth patterns and body compositions at various stages of development, leading to different BMI percentiles.
How Paediatric BMI is Interpreted (by Professionals)
Healthcare providers use the following percentile ranges from CDC or WHO growth charts to classify a child's weight status:
- Underweight: BMI below the 5th percentile
- Healthy Weight: BMI between the 5th and 85th percentile
- Overweight: BMI between the 85th and 95th percentile
- Obese: BMI at or above the 95th percentile
These percentiles indicate how a child's BMI compares to other children of the same age and sex. For example, a child at the 75th percentile means their BMI is greater than 75% of children of the same age and sex in the reference population.
Calculating Paediatric BMI
The formula for BMI is the same for both children and adults:
BMI = weight (kg) / [height (m)]2
Or, if using pounds and inches:
BMI = [weight (lbs) / [height (inches)]2] * 703
Our calculator handles these conversions automatically to provide the BMI value.
Importance of Monitoring Paediatric BMI
Regular monitoring of a child's BMI can help identify potential weight-related health issues early on. Being overweight or obese in childhood can lead to various health problems, including:
- Type 2 diabetes
- High blood pressure
- High cholesterol
- Joint problems
- Sleep apnea
- Psychological issues like low self-esteem and depression
Conversely, being underweight can also indicate underlying health or nutritional issues.
Limitations and What to Do Next
While this calculator provides a useful screening tool, it's crucial to remember its limitations:
- It does not account for muscle mass, which can sometimes lead to a higher BMI in very athletic children.
- It is a screening tool, not a diagnostic tool.
Always consult with a pediatrician or healthcare provider to discuss your child's BMI, growth chart percentiles, and overall health. They can provide personalized advice and guidance based on a comprehensive assessment of your child's health history, diet, physical activity, and family medical history.
Examples of Paediatric BMI Calculation:
Example 1: A 7-year-old boy, 6 months old, weighs 25 kg and is 120 cm tall.
- Weight in kg: 25 kg
- Height in meters: 120 cm / 100 = 1.2 m
- BMI = 25 / (1.2 * 1.2) = 25 / 1.44 = 17.36
- (A healthcare professional would then plot this BMI on a growth chart for a 7.5-year-old boy to determine his percentile.)
Example 2: A 10-year-old girl, 0 months old, weighs 40 kg and is 140 cm tall.
- Weight in kg: 40 kg
- Height in meters: 140 cm / 100 = 1.4 m
- BMI = 40 / (1.4 * 1.4) = 40 / 1.96 = 20.41
- (This BMI would be plotted on a growth chart for a 10-year-old girl to determine her percentile.)