This tool is educational and does not replace professional assessment or official reports. The values shown are estimates based on population-level criteria and may not reflect your individual body composition.

Biological sex

Male

Female

Weight (kg)

Height (cm)

Age (years) — optional, for context

Educational Results

BMI
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kg/m²

WHO Classification

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BMI classification scale:

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Classification	BMI (kg/m²)
Underweight	< 18,5
Normal weight	18,5 – 24,9
Overweight	25,0 – 29,9
Obesity grade I	30,0 – 34,9
Obesity grade II	35,0 – 39,9
Obesity grade III	≥ 40,0

Important Notice: This content and the tool on this page are intended exclusively for educational and informational purposes. They do not replace consultation, diagnosis, tests, reports, or treatment. Clinical decisions require in-person evaluation and individualized analysis by qualified professionals. For any course of action, consult your doctor.

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What is Body Mass Index (BMI)?

Body Mass Index (BMI) is a simple measure that relates body weight to height. It is obtained by dividing weight in kilograms by the square of height in meters (BMI = weight / height²). Created in 1832 by the Belgian mathematician Adolphe Quetelet, it became a widely used tool in public health for epidemiological screening of overweight and obesity.

The World Health Organization (WHO) adopts BMI classification criteria to standardize the assessment of body composition at the population level. This classification is useful for identifying risk categories, but it should always be interpreted within a broader clinical context.

How is BMI calculated?

The formula is simple: divide your weight (in kg) by the square of your height (in meters). Example: a person weighing 75 kg and 1.70 m tall will have a BMI of 75 ÷ (1.70 × 1.70) = 75 ÷ 2.89 = 25.95 kg/m². This calculator performs the calculation automatically.

Important limitations of BMI

Although it is a quick and accessible tool, BMI has significant limitations that every user should be aware of:

It does not distinguish muscle mass from body fat: Athletes and very muscular people may have a high BMI without having excess body fat.
It does not account for fat distribution: BMI does not distinguish between subcutaneous fat (under the skin) and visceral fat (around the internal organs). Visceral fat is associated with greater metabolic risks.
Variations by age and sex: Body composition varies naturally between sexes and throughout aging. Older adults and children have different body characteristics that are not adequately captured by simple BMI.
It is not an individual diagnosis: BMI is an epidemiological tool for identifying population patterns, not an individual health diagnosis.
It does not consider genetic factors: Genetic variations, body type, and basal metabolism are not reflected in the calculation.

When is BMI useful?

BMI is particularly useful for: epidemiological screening in populations; quick triage to identify individuals who may benefit from a more detailed evaluation; clear communication of risk criteria in clinical research; public health protocols and preventive campaigns.

More comprehensive approach

For a truly effective assessment of body composition and health, it is necessary to combine: waist circumference measurements and fat distribution; body composition analysis (body fat percentage, muscle mass); assessment of cardiorespiratory fitness; laboratory tests (glucose, lipids, inflammation); complete clinical history; assessment of lifestyle habits and family history; blood pressure and other health markers.

Frequently Asked Questions

Is BMI reliable for everyone?

No. BMI has significant limitations for athletes, elderly people, children, and pregnant women. Athletes may have elevated BMI due to greater muscle mass. Elderly often have lower bone density and different fat distribution patterns. Children need specific BMI curves by age and sex (WHO z-scores). Pregnant women present physiological changes not adequately reflected in simple BMI.

What is the difference between BMI and body composition?

BMI is simply a relationship between weight and height. Body composition refers to the proportion of fat, muscle, bone, and water in the body. Two people with the same BMI can have completely different body compositions. Body composition is assessed by methods such as bioimpedance, DEXA, MRI, or more detailed anthropometric measurements.

Does BMI change with age?

Yes. As we age, body composition changes: there is loss of muscle mass (sarcopenia) and fat redistribution. Therefore, two individuals with the same BMI may have different degrees of metabolic risk if they are different ages. Studies suggest that BMI in elderly may be less predictive of health risk than in younger adults.

Can I use BMI to define my diet?

No. BMI is just a number and should not be the only criterion for dietary changes. Defining an appropriate diet requires individualized professional assessment, considering: complete clinical history; body composition assessment; laboratory tests; specific health goals; food and cultural preferences; medical conditions; use of medications.

Is BMI appropriate for children?

Simple adult BMI is not appropriate for children. WHO and health agencies use specific growth curves by age and sex, expressed as z-scores (how many standard deviations above or below the median for the age). If evaluating a child, consult a pediatrician and use the recommended curves for the age group.

What is the real relationship between BMI and health?

BMI is an epidemiological tool, not diagnostic. Populations with higher BMI, on average, have greater prevalence of metabolic diseases. But this does not mean that individuals with elevated BMI necessarily have these diseases, or that those with normal BMI are risk-free. Health is multidimensional and requires holistic assessment by a qualified professional.

Scientific References

World Health Organization. Obesity and overweight. Fact Sheet. WHO, 2024. who.int
Keys A, Fidanza F, Karvonen MJ, et al. Indices of relative weight and obesity. J Chronic Dis. 1972;25(6):329-343. PubMed
Flegal KM, Kit BK, Orpana H, Graubard BI. Association of all-cause mortality with overweight and obesity using standard body mass index categories. JAMA. 2013;309(1):71-82. PubMed
Associação Brasileira para o Estudo da Obesidade e Síndrome Metabólica (ABESO). Diretrizes Brasileiras de Obesidade 2016. abeso.org.br
Nuttall FQ. Body Mass Index: Obesity, BMI, and Health: A Critical Review. Nutr Today. 2015;50(3):117-128. PubMed

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Important: This content is exclusively educational and must not, under any circumstances, be used for self-diagnosis or treatment. It does not replace consultation with a qualified health professional. Responsibility for the use of the information presented here lies entirely with the user.

I transparently declare that I have no conflict of interest with any pharmaceutical companies that may be mentioned. When I cite brand names or patented products, I do so solely to facilitate understanding by the lay public and make medical knowledge more accessible.

All content on this site is intended to inform, educate, and clarify — always free of charge.

I emphasize that none of the information shared here should be used as an isolated criterion for assessment, diagnosis, or therapeutic management without proper professional guidance. Each person is unique and must be evaluated individually. Improper use of this information, without specialized follow-up, can pose serious health risks.