Child BMI Percentile Calculator
For children and teens, BMI is interpreted against age- and sex-specific CDC growth charts. This tool computes the BMI number and an illustrative percentile band; consult a pediatrician for an exact percentile and any health decisions.
The Child BMI Percentile Calculator computes the body mass index of a child or teenager from their weight and height, then explains how that number is interpreted. Unlike adults, children are not judged against fixed BMI ranges; instead a pediatric BMI is plotted on CDC growth charts that account for age and sex. This tool gives you the BMI figure and describes the percentile bands so you understand what a clinician looks for.
Formula
BMI = 703 × weight ÷ height²
- weight
- Child body weight in pounds
- height
- Child height in inches
- 703
- Conversion factor for imperial (pound and inch) BMI
How it works
- Enter the child weight in pounds and height in inches.
- The calculator applies the imperial BMI formula, multiplying weight by 703 and dividing by height squared, then rounds to one decimal.
- It maps the result to an illustrative category and the percentile band a pediatrician would use, since the true band depends on the child exact age and sex.
Worked example
A child weighing 70 lb and standing 54 inches (4 ft 6 in) tall.
- Height squared = 54 × 54 = 2,916.
- BMI = 703 × 70 ÷ 2,916 = 16.88.
- Rounded to one decimal, BMI = 16.9, which falls in the healthy-weight band.
BMI of 16.9, interpreted in the 5th to 84th percentile (healthy weight) band.
Frequently asked questions
- Why is child BMI judged by percentile instead of fixed numbers?
- Children grow rapidly and body composition changes with age and sex. A BMI that is healthy for a 6-year-old may be high for a 16-year-old, so pediatric BMI is ranked against peers of the same age and sex using percentile charts.
- What percentile is considered a healthy weight?
- The CDC generally considers the 5th to 84th percentile a healthy weight, the 85th to 94th overweight, and the 95th percentile or above obese. Below the 5th percentile is classed as underweight.
- Should I use this number for medical decisions?
- No. This calculator gives an estimate and an illustrative band only. An exact, age- and sex-adjusted percentile and any health decision should come from a pediatrician using official growth charts.