BMI Calculator — Body Mass Index & WHO Category

Your estimated BMI

26.1

WHO category: overweight

BMI cannot tell muscle from fat. Muscular and athletic people are routinely classed as overweight despite low body fat — if that might be you, a body-fat estimate is a much better guide than BMI.

BMI is a population screening estimate, not a diagnosis. Discuss what your number means for you with a health professional.

Methodology

Body mass index is weight divided by height squared:

BMI = weight (kg) ÷ height (m)²

Results are classed against the World Health Organization's adult categories:

BMI (kg/m²)	WHO category
< 18.5	Underweight
18.5 – 24.9	Healthy weight
25.0 – 29.9	Overweight
30.0 – 34.9	Obesity class I
35.0 – 39.9	Obesity class II
≥ 40.0	Obesity class III

Interpreting your result

BMI is best understood as a population screening measure: across large groups it correlates with body fat and with health risk, which is why health services still use it. For an individual, it is a starting point for a conversation, not a conclusion — it knows nothing about your body composition, training history, frame or ethnicity.

The athlete problem deserves emphasis: because muscle is denser than fat, muscular people routinely register as overweight — many elite rugby players and sprinters are technically obese by BMI. If you train seriously, a body-fat estimate (see our US Navy calculator) tells you far more than BMI can.

Limitations

BMI cannot distinguish fat from muscle, nor say where fat is carried — and central (abdominal) fat carries most of the metabolic risk.
The WHO notes that risk thresholds sit lower for some Asian populations; a single set of global cut-offs fits nobody perfectly.
Adult cut-offs do not apply to children, adolescents or pregnancy.
At the individual level, waist circumference, body-fat percentage and clinical markers measured with your GP are all more informative than a height-to-weight ratio from 19th-century statistics.

Sources

Pull the receipts — 2 cited sources

FitTools · sources

Every formula cited ✓

Frequently asked questions

What is a healthy BMI?

For adults, the WHO classifies a BMI of 18.5 to 24.9 as the healthy-weight range, 25 to 29.9 as overweight, and 30 or above as obesity, split into classes I–III. These are population screening bands rather than individual diagnoses.

How is BMI calculated?

BMI is your weight in kilograms divided by your height in metres squared. A 80 kg person at 1.75 m has a BMI of 80 ÷ 1.75² ≈ 26.1.

Is BMI accurate for muscular people?

No — this is BMI's best-known weakness. It cannot tell muscle from fat, so muscular athletes are routinely classed as overweight or even obese despite low body fat. If you carry meaningful muscle, a body-fat estimate is a far better guide.

Does BMI apply to children or during pregnancy?

This calculator uses adult cut-offs and is not valid for children, teenagers or pregnancy. Children's BMI is assessed against age- and sex-specific growth charts by health professionals.

Why do doctors still use BMI?

At a population level BMI correlates well with health risk and is essentially free to measure, which makes it useful for screening. Its limits appear at the individual level, which is why results here are framed as an estimate to discuss with a professional, not a verdict.

Free body fat calculator using the US Navy circumference method (Hodgdon & Beckett 1984). Tape-measure inputs, metric and imperial, with the ±3–4 point error band shown honestly.

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