How is BMI calculated?

BMI = bodyweight in kg divided by height in metres squared. The arithmetic is unambiguous; individual interpretation is limited.

What do the WHO categories mean?

They are standardized adult screening categories. They do not describe individual body composition and do not replace a health assessment.

Why can BMI be misleading for muscular people?

Because the equation only knows total bodyweight and height. Added muscle raises bodyweight just like other tissue, and BMI cannot distinguish the cause.

Are body fat or FFMI automatically better?

They answer different questions but have their own measurement and model error. No single metric provides a complete health or body assessment on its own.

Can I derive a target weight from BMI alone?

Not sensibly as an individual recommendation. Body composition, health context and personal goals are absent from the equation.

Calculator · BMI Calculator

BMI calculator: what does my body-mass index tell me?

The BMI calculator relates your body weight to your height. The value is a rough statistical classification and says nothing about your body composition.

Result

BMI: 24.7kg/m²
WHO category: Normal weight

BMI is a WHO screening classification based on weight and height. It does not distinguish body fat from fat-free mass, so individual interpretation — especially with unusual body composition — is limited.

BMI is a coarse screening measure based on weight and height. Do not read the WHO category as a diagnosis or as a measure of body composition.

Method

How the calculation works

BMI is calculated as weight (kg) divided by height (m) squared. The calculator takes your inputs and places the result in the categories defined by the WHO.

Categories range from underweight (below 18.5) through normal weight (18.5–24.9) and overweight (25–29.9) to three obesity classes from 30 upwards. No other factors like muscle mass or body-fat enter the formula.

Methodology: formulas, assumptions and estimate confidence →

Estimate confidence

How reliable is this estimate?

High

BMI arithmetic and WHO categorization are deterministic. Its ability to describe individual body composition or health is much more limited.

What the levels mean →

Interpretation

How to read your result

WHO categories are adult screening categories, not a diagnosis of individual health or body composition. BMI only describes the mathematical relationship between bodyweight and height.

With high muscle mass or other unusual body composition, the same BMI category can represent very different physical situations. Additional clinical or anthropometric information must be considered separately.

Limits

Where this calculator ends

BMI does not distinguish fat mass, muscle, bone or water. It is therefore not a body-fat or fitness measure.

Children and adolescents require age- and sex-specific approaches. Pregnancy and other special circumstances also need different interpretation; this calculator is intended as a general adult screening tool.

Common mistakes

01Reading the WHO category as an individual diagnosis.
02Equating BMI with body-fat percentage.
03Assuming a high BMI reveals why bodyweight is high.
04Deriving a personal target weight from BMI alone.
05Applying adult cutoffs uncritically to children, adolescents or pregnancy.

Example

A worked example

180 cm, 80 kg

BMI ≈ 24.7 → normal weight per the WHO. A typical classification for a moderately trained person — real body composition at the same BMI can look very different.

FAQ

Frequently asked questions

How is BMI calculated?: BMI = bodyweight in kg divided by height in metres squared. The arithmetic is unambiguous; individual interpretation is limited.
What do the WHO categories mean?: They are standardized adult screening categories. They do not describe individual body composition and do not replace a health assessment.
Why can BMI be misleading for muscular people?: Because the equation only knows total bodyweight and height. Added muscle raises bodyweight just like other tissue, and BMI cannot distinguish the cause.
Are body fat or FFMI automatically better?: They answer different questions but have their own measurement and model error. No single metric provides a complete health or body assessment on its own.
Can I derive a target weight from BMI alone?: Not sensibly as an individual recommendation. Body composition, health context and personal goals are absent from the equation.

Sources

01World Health Organization. Diet, Nutrition and the Prevention of Chronic Diseases. WHO Technical Report Series 916. 2003. Adult BMI classification: underweight <18.5, normal range 18.5–24.9, overweight ≥25 and obesity ≥30 kg/m².

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