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BMI Calculator Online

Calculate an adult Body Mass Index screening estimate in metric or imperial units and compare it with standard adult BMI reference categories.

Adult BMI screening categories

Below 18.5
Underweight
18.5 – 24.9
Normal weight
25.0 – 29.9
Overweight
30.0 – 34.9
Obese Class I
35.0 – 39.9
Obese Class II
40.0 and above
Obese Class III
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About This Tool

What it does

Calculates adult BMI from height and weight, then shows the standard adult screening category and the weight interval corresponding mathematically to BMI 18.5–24.9 for that height.

Who it's for

Adults using BMI as a general screening reference. It is not intended for children, pregnancy, diagnosis or personalised weight targets.

Your privacy

Your height and weight are never sent to any server. All calculations happen locally in your browser. Nothing is stored.

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International guidance and limitations

BMI is a height-to-weight screening measure for adults. It does not directly measure body fat, diagnose a condition or set an individual target. Age, pregnancy, muscularity, ethnicity and clinical context can affect interpretation.

Sources reviewed 23 June 2026: World Health Organization: obesity and overweight; US CDC: adult BMI categories.

Frequently Asked Questions

Metric BMI is weight in kilograms divided by height in metres squared. The calculator converts pounds, feet and inches to the same metric formula before rounding the result to one decimal place.
Standard adult screening categories use below 18.5, 18.5–24.9, 25.0–29.9 and 30 or above. They are population screening references, not a diagnosis or a personalised target.
It is the mathematical weight interval at the entered height that corresponds to BMI 18.5–24.9. It is a screening reference only and should not be interpreted as a required target.
No. Children and teenagers require age- and sex-specific growth references, and BMI is interpreted differently during pregnancy.
Yes. BMI does not distinguish fat, muscle, bone or fluid, so it can give a higher category to some muscular people and cannot assess fat distribution or individual health.
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