KidBMI

Child BMI Calculator

BMI for kids and teens, with a reminder to check age-specific percentiles.

Weight (kg)

Height (cm)

Age (years)

BMI

17.752

For children, always compare against age-specific CDC percentile charts.

Category (adult scale): Underweight

What you entered

Weight (kg): 30Height (cm): 130Age (years): 10

1
Convert height to metres
h = 130 cm ÷ 100= 1.30 m
2
Square the height
h² = 1.30²= 1.6900 m²
3
Divide weight by height²
BMI = 30 kg ÷ 1.6900 m²= 17.8
4
Compare to WHO ranges
Underweight <18.5 · Healthy 18.5–24.9 · Overweight 25–29.9 · Obese 30+= Underweight

Result

BMI: 17.752

At 30 kg and 130 cm (age 10), BMI is 17.8 on the adult scale — always cross-check against age-specific CDC percentile charts for children.

BMI for common child and teen height and weight combinations

BMI is the same arithmetic at every age: weight in kilograms divided by height in metres squared. These rows walk from a small child up to a full-grown teenager, so you can find one close to your own measurements.

Height (cm)	Weight (kg)	Weight (lb)	BMI
110	18	40	14.9
120	23	51	16.0
130	28	62	16.6
140	34	75	17.3
150	42	93	18.7
155	46	101	19.1
160	50	110	19.5
165	55	121	20.2
170	60	132	20.8

The BMI number is the answer here; the adult label is not. Adult cut-offs, where 18.5 to 24.9 counts as healthy, do not apply to children, so a healthy 8-year-old with a BMI of 16 is entirely normal even though 16 reads as underweight on the adult scale. Interpreting a child's BMI requires a CDC or WHO percentile chart for their exact age and sex, and whether they keep tracking along their own growth curve matters far more than any single reading. Take any concern to a pediatrician rather than acting on this number.

Why kids need percentiles, not fixed categories

A growing child's healthy BMI shifts constantly with age and sex — pediatricians use percentile charts that compare a child to others their exact age, rather than the fixed adult 18.5–24.9 healthy range.

Use this as a starting point only

This calculator gives the raw BMI number, but interpreting it for a child always requires comparing against age-specific CDC growth charts — a pediatrician is the right resource for any real concern.

Frequently asked questions

How is child BMI different from adult BMI?

The formula is the same (weight ÷ height²), but interpretation differs. Adults use fixed categories (18.5–24.9 = normal). Children use age-and-sex-specific percentiles: underweight < 5th, healthy 5th–85th, overweight 85th–95th, obese ≥ 95th. A BMI of 18 might be normal for a 12-year-old but underweight for an adult.

What BMI percentile is healthy for a child?

The 5th to 85th percentile is considered healthy weight. Below 5th is underweight, 85th–95th is overweight, and above 95th is obese. These percentiles compare your child to others of the same age and sex in CDC reference data. A child tracking along their own growth curve consistently is generally healthy.

Should I worry if my child's BMI is high?

Not necessarily — children go through natural growth spurts where BMI fluctuates. A single reading matters less than the trend over time. If BMI consistently tracks above the 85th percentile, discuss it with your pediatrician. They'll consider growth velocity, puberty stage, family history, and activity level.