BMI Calculator

This tool calculates Body Mass Index (BMI) from the height and weight you enter. It also displays the Ponderal Index, a separate height-and-weight ratio. Select the unit tab that matches your measurements.

What BMI tells you

Body Mass Index is a ratio of weight to height squared. It is commonly used as a simple screening measure in population health and as one part of an adult health assessment. It does not measure body fat directly and cannot, on its own, establish whether a person is healthy or diagnose a medical condition.

Interpretation depends on age and the reference system being used. The adult categories below are commonly used for adults aged 20 years and older. They are screening categories, not individual treatment targets.

Adult BMI reference categories

The following conventional WHO adult classification uses BMI expressed in kilograms per square metre. Boundary values are shown to make the categories easier to read; small differences in rounding may occur.

Category	BMI (kg/m2)
Severe thinness	Below 16.0
Moderate thinness	16.0 to below 17.0
Mild thinness	17.0 to below 18.5
Normal range	18.5 to below 25.0
Overweight	25.0 to below 30.0
Obesity class I	30.0 to below 35.0
Obesity class II	35.0 to below 40.0
Obesity class III	40.0 or higher

Adult BMI chart

This chart is a visual guide to the adult BMI groupings. It does not account for body composition, medical history or other factors that a clinician may consider.

BMI-for-age in children and adolescents

For children and adolescents, BMI is interpreted using age- and sex-specific growth references rather than the fixed adult categories. This page's percentile calculation uses the US Centers for Disease Control and Prevention (CDC) 2000 BMI-for-age reference data for ages 2 through 19. These references describe a US population and may not represent every country's population equally well. A percentile is a comparison with the reference population, not a diagnosis.

CDC BMI-for-age category	Percentile
Underweight	Below 5th
Healthy weight	5th to below 85th
Overweight	85th to below 95th
Obesity	95th or higher

Official CDC growth-chart resources: CDC clinical growth charts and boys' BMI-for-age chart / girls' BMI-for-age chart.

Why BMI is only one part of an assessment

BMI does not distinguish fat mass from muscle, bone or other body tissues, and it does not show where body fat is distributed. A person with substantial muscle mass may have a higher BMI without having the same body-fat profile as another person with that BMI. Age, pregnancy, fluid retention, health conditions, medication, ethnicity and other factors can also affect how a result should be interpreted.

A clinician may consider additional information such as waist measurement, blood pressure, medical history, laboratory results, physical activity and changes over time. Do not use a BMI value alone to decide whether to start a diet, change medication or pursue treatment.

Understanding health risks

At a population level, BMI outside commonly used reference ranges can be associated with different health risks. The relationship is not identical for every person, and BMI cannot predict an individual's health outcome. A healthcare professional can interpret a result alongside other relevant information.

Formulas used by this calculator

The calculator uses standard unit-conversion formulas:

Worked example

For a height of 1.70 metres and a weight of 65 kilograms, BMI = 65 ÷ (1.70 × 1.70), which is approximately 22.5 kg/m². This arithmetic example illustrates the formula; it is not an assessment of an individual's health.

Sources and reference notes

• World Health Organization — Body mass index, for adult BMI reference information.
• US CDC — Child and Teen BMI Calculator, for age- and sex-specific interpretation.
• US CDC — Growth Charts, for the growth reference framework used by this implementation.

This tool is for general education and screening information only. It does not diagnose a condition or replace an assessment by a qualified healthcare professional. The child and teen percentile option uses US CDC reference data and may not be appropriate as a standalone assessment for children in other populations. If you have concerns about your weight or a child's growth, speak with a qualified healthcare professional.

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