BMI Calculator Kids: A Simple Health Tool for Your Child

Calculate your child's BMI and percentile ranking (ages 2-19)

This tool calculates a child's BMI from height and weight, then ranks it against growth percentiles for their age and gender (ages 2–19), in metric or imperial units.

Why a Child's BMI Isn't Read Like an Adult's

Take a 12-year-old boy who is 140 cm tall and weighs 42 kg: BMI = 42 ÷ 1.40² = 42 ÷ 1.96 ≈ 21.4. On the fixed adult scale, a BMI of 21.4 is squarely "Normal weight." But this calculator's percentile data for 12-year-old boys puts the 85th percentile at a BMI of 19.7 and the 95th at 23.3 — so a BMI of 21.4 actually lands around the 90th percentile for a boy that age, which is classified as Overweight. That gap is exactly why fixed adult BMI cutoffs don't work for growing kids, and why this tool compares against age- and gender-specific percentile bands instead.

Step-by-Step Instructions

  1. Choose metric (kg/cm) or imperial (lbs/ft/in).
  2. Enter age (2–19) and gender.
  3. Enter height and weight.
  4. Click "Calculate BMI."

Reading the Result

The output gives BMI to one decimal, a percentile, and a weight status: below the 5th percentile is Underweight, 5th to 84th is Healthy weight, 85th to 94th is Overweight, and 95th and above is Obese.

Limitations

This is a screening tool built on a simplified reference table, not a clinical growth chart. It does not replace advice from a health professional — many other factors affect a child's health, so consult a healthcare provider for a full assessment.

Common Use Cases

Parents checking growth status between doctor visits, or school nurses running a quick, rough screening — not a diagnostic measurement.