BMI Calculator for Kids - Child Body Mass Index Calculator

Body mass index (BMI) describes weight relative to height. Children and adolescents grow and change body composition, so a raw BMI number cannot establish a weight category. This calculator gives the arithmetic value only.

BMI equals weight in kilograms divided by height in meters squared. With pounds and inches, BMI equals weight divided by height squared, multiplied by 703. Accurate measurements matter more than extra decimal places.

For ages 2–19, a clinician compares BMI with a sex-specific BMI-for-age growth chart using age in months. The chart, growth history, and clinical context are needed before discussing weight status. This page does not calculate a percentile, category, or target weight.

A BMI-for-age percentile compares a child's BMI with BMIs for children of the same age and sex in the chart's reference population. It does not say that the child weighs more than that percentage of peers. A raw BMI value is not itself a percentile.

A series of measured heights and weights gives a clinician more context than one measurement. Puberty and individual growth patterns can change BMI. If growth or weight concerns you, bring the measurements and their dates to a pediatric clinician.

Offer a variety of foods, opportunities for enjoyable physical activity, and adequate sleep. Avoid setting a diet or target weight from this calculator's raw BMI value; discuss concerns with a pediatric clinician.

BMI does not directly measure body fat or diagnose health. This tool lacks the birth date, measurement date, sex-specific chart data, and extended chart calculation needed for pediatric BMI-for-age interpretation.

In CDC's worked example, a 13-year-old girl who is 60 inches tall and weighs 175 pounds has a BMI of 34.2. Using her age and sex with the extended growth chart, CDC places that BMI at the 99.2nd percentile and in the severe-obesity category. This calculator provides the BMI value but does not perform that chart-based interpretation. CDC interpretation and examples.