BMI (Clinical)

Calculate Body Mass Index with clinical obesity classifications.

Last reviewed: July 2026How we build & verifyEstimate only. Verify important decisions with a qualified professional

Weight (kg)

Height (cm)

How it works

Divides body mass by the square of height to place a patient in a clinical weight band, splitting obesity into classes I, II and III rather than stopping at a single obese label. The result is a screening figure that decides whether to look further, not a diagnosis.

Formula

BMI = weight(kg) / height(m)²

Variables

weightbody mass in kilograms
heightstanding height in metres (centimetres ÷ 100)
BMIthe ratio, in kg/m², compared against a category table

Worked example

Inputs: 82 kg, 172 cm

Convert height to metres: 172 / 100 = 1.72
1.72² = 2.9584
82 / 2.9584 = 27.72

Result: BMI 27.7, which falls in the overweight band on WHO cut-offs

Notes

WHO bands: below 18.5 underweight, 18.5 to 24.9 normal, 25 to 29.9 overweight, 30 to 34.9 obesity class I, 35 to 39.9 class II, 40 and above class III.
Lower thresholds apply to South Asian, Chinese and several other Asian populations, where diabetes and cardiovascular risk appear at a lighter weight for the same height: 23 marks the overweight action point and 27.5 the obese one. India adopted those figures in its 2009 consensus guidelines. The 27.7 above therefore reads as overweight under WHO and as obese under the Asian cut-offs, and the clinical response differs accordingly.
BMI counts total mass and cannot separate muscle from fat, or subcutaneous fat from the visceral fat that actually drives metabolic risk. A lean rugby forward and a sedentary adult of identical height and weight receive identical scores. Waist circumference or waist-to-height ratio supplies the distribution information BMI has no access to.
Height is routinely self-reported too high and genuinely shrinks with age, and it enters the formula squared, so a 3 cm error at 1.72 m moves the result by about 1 point. Measure it.

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Frequently Asked Questions

No. Bmi Clinical is free, with no signup required, and nothing you enter leaves your browser.

Bmi Clinical is built on published formulas and reference ranges from established health sources. We revisit it periodically as guidance evolves; the "Last reviewed" date above shows when that last happened. If something looks wrong, tell us with the feedback button in the bottom-right corner.

No. Bmi Clinical gives you a general estimate based on the inputs you provide, not a diagnosis. Existing conditions, medications, and individual history all change what a number actually means for you. Treat this as a starting point for a conversation with a doctor or other qualified health professional, not a substitute for one.