BMI Calculator for Kids: How to Check Your Child’s BMI

A BMI calculator for kids checks a child’s body mass index using height and weight. CDC notes that child BMI is interpreted using sex-specific BMI-for-age.

What is BMI for kids?

BMI, or Body Mass Index, is a simple number calculated using a child’s weight and height. For children, BMI is not read the same way as adult BMI. Instead, it is compared with children of the same age and gender to understand where the child falls on a growth chart.

This is why a child BMI calculator usually asks for: Age, Gender, Height and Weight.

For Indian users, the most useful format is usually height in cm and weight in kg.

How to calculate BMI for kids

The BMI formula is:

BMI = weight in kg ÷ height in metres²

Example: If a child weighs 25 kg and is 1.25 m tall:

BMI = 25 ÷ (1.25)² = 16

But for kids, the BMI number alone is not enough. It should be interpreted with age and gender using a child BMI chart or percentile reference. CDC explains that child and teen BMI calculators report BMI, BMI percentile and BMI category.

Is BMI enough to know if a child is healthy?

No. BMI is only a screening tool. It does not directly measure body fat, muscle, diet quality, activity, sleep, medical history or growth pattern. NHS also notes that a child BMI calculator does not tell the difference between muscle and fat or diagnose a condition.

Use BMI as a starting point, not a final answer.

When should parents speak to a doctor?

Speak to a paediatrician if:

• Your child’s BMI is very low or very high
• Weight changes are sudden
• Your child has low energy, poor appetite or frequent tiredness
• You are worried about eating habits or growth
• The BMI result does not match how your child looks, eats or behaves

HealthyChildren notes that BMI is just one part of the health picture and that a paediatrician can guide parents based on the child’s full growth and health context.

Frequently Asked Questions on BMI

What is a BMI calculator for kids?

A BMI calculator for kids estimates a child’s BMI using height and weight, then helps interpret it based on age and gender.

Can I calculate BMI for kids in kg and cm?

Yes. Enter weight in kilograms and height in centimetres. The calculator converts height into metres to calculate BMI.

What is a healthy BMI for kids?

For children, a healthy BMI is usually between the 5th and less than 85th BMI-for-age percentile.

Should I calculate BMI for kids under 5?

BMI-for-age charts exist for younger children too, including WHO BMI-for-age standards. However, for very young children, growth should be interpreted by a doctor or trained healthcare professional. WHO provides BMI-for-age charts and tables for boys and girls.

Is BMI a diagnosis?

No. BMI is a screening tool. It should not be used alone to diagnose a child’s health condition.