What are the assumptions of the IMC formula?

Adults 20 years or older. For children and teens, BMI is age- and sex-specific (percentile). Standard WHO BMI categories apply. Asian populations may need different cutoffs (per WHO 2004). Height and weight are accurate measurements (self-reported values reduce accuracy).

What are the limitations of IMC?

BMI does not distinguish between muscle mass and fat mass. Athletes often have high BMI but low body fat. BMI does not account for fat distribution. Visceral (belly) fat is more dangerous than subcutaneous fat. BMI may misclassify older adults (who tend to lose muscle) and pregnant women. Ethnic differences in body composition mean standard cutoffs may not apply equally to all groups.

Méthodologie

How we calculate BMI

Our methodology for the IMC calculator: the formula, step-by-step calculation, authoritative sources, and limitations. Reviewed quarterly.

Formule

BMI = weight (kg) / height (m)²

Étape par étape

1
Convert weight to kilograms (1 lb = 0.4536 kg).
2
Convert height to meters (1 in = 0.0254 m; 1 ft = 0.3048 m).
3
Square the height in meters (multiply it by itself).
4
Divide the weight in kilograms by the squared height.
5
The result is your BMI in kg/m². Compare to WHO categories.

Sources autorisées

Every claim on this page is backed by an authoritative source.

Hypothèses

What we take to be true when applying this formula.

Adults 20 years or older. For children and teens, BMI is age- and sex-specific (percentile).
Standard WHO BMI categories apply. Asian populations may need different cutoffs (per WHO 2004).
Height and weight are accurate measurements (self-reported values reduce accuracy).

Limites

What this method does NOT capture.

BMI does not distinguish between muscle mass and fat mass. Athletes often have high BMI but low body fat.
BMI does not account for fat distribution. Visceral (belly) fat is more dangerous than subcutaneous fat.
BMI may misclassify older adults (who tend to lose muscle) and pregnant women.
Ethnic differences in body composition mean standard cutoffs may not apply equally to all groups.

Note éditoriale

Reviewed against WHO 2004 expert consultation and CDC 2023 guidelines.

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Dernière révision: 2026-06-15 • Reviewed by: CalcxApp editorial team