Is a standard BMI calculator accurate for children?

No. Adult BMI categories do not apply to children and teens, who need age- and sex-specific BMI percentile charts instead, since what counts as normal changes as kids grow.

BMI Calculator — Body Mass Index & Weight Range

Q: What is a healthy BMI?

The World Health Organization's Normal weight range is a BMI between 18.5 and 24.9. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese, further split into Class I, II, and III.

Q: Is BMI accurate for athletes or muscular people?

Not reliably. BMI only uses height and weight, so it cannot distinguish muscle mass from fat mass, and a lean muscular person can be misclassified as overweight or obese. Body-fat percentage or waist circumference are better indicators in that case.

Q: Does BMI work the same for men and women?

The standard BMI formula and WHO categories do not adjust for sex, even though men and women typically carry body fat differently at the same BMI. It is still used as a simple, sex-neutral screening tool for adults.

Calculate your BMI

Your BMI
Category
Healthy weight range

How this is calculated

BMI is weight divided by height squared (kg/m² in metric, or 703 × lb/in² in US units — the 703 constant just converts pounds and inches into the same kg/m² scale). The category thresholds (Underweight, Normal, Overweight, Obese Class I/II/III) are the World Health Organization's standard adult BMI ranges. The healthy weight range shown is simply the weight your exact height would need to be to land in the "Normal weight" band (BMI 18.5-24.9).

BMI's real limitations

BMI is a quick population-level screening tool, not a diagnosis. It doesn't distinguish muscle from fat, so a muscular athlete can show as "overweight" despite low body fat, and it isn't designed for children, teenagers, pregnant women, or adults over 65, all of whom need different reference standards. Two people with an identical BMI can have very different body compositions and health risk. Use it as a starting data point, not a verdict — a doctor or a body-fat measurement gives a much fuller picture.

Frequently asked questions

What is a healthy BMI?

The WHO's "Normal weight" range is a BMI between 18.5 and 24.9. Below 18.5 is classified as underweight, 25-29.9 as overweight, and 30+ as obese (further split into Class I, II, and III).

Is BMI accurate for athletes or muscular people?

Not reliably. Since BMI only uses height and weight, it can't tell muscle mass from fat mass, so a lean, muscular person can be misclassified as overweight or obese. Body-fat percentage or waist circumference are better indicators in that case.

Does BMI work the same for men and women?

The standard BMI formula and WHO categories don't adjust for sex, even though men and women typically carry body fat differently at the same BMI. It's still used as a simple, sex-neutral screening tool for adults.

Is this calculator accurate for kids?

No — this tool uses the adult BMI categories. Children and teens need age- and sex-specific BMI percentile charts instead, since what's "normal" changes significantly as kids grow. Check with a pediatrician for a child's healthy weight range.