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BMI Calculator (Body Mass Index)

Calculate your Body Mass Index (BMI) and find out if your weight is within the healthy range according to WHO standards.

Sources: WHO -- Obesity and Overweight Fact Sheet · NIH -- Calculate Your Body Mass Index

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How to Calculate BMI (Body Mass Index)

BMI, or Body Mass Index, is the most widely used indicator worldwide to assess whether a person's weight is appropriate for their height. The World Health Organization (WHO) recommends it as a screening tool to classify underweight, normal weight, overweight, and obesity in adults.

The BMI Formula

The formula is straightforward:

BMI = Weight (kg) / Height (m)^2

For example, a person weighing 70 kg who is 1.75 m tall would have a BMI of 70 / (1.75 x 1.75) = 22.9 -- normal weight.

WHO Classification Categories

The WHO defines these categories for adults (over 18):

  • Underweight: BMI < 18.5
  • Normal weight: BMI 18.5 - 24.9
  • Overweight: BMI 25.0 - 29.9
  • Obesity class I: BMI 30.0 - 34.9
  • Obesity class II: BMI 35.0 - 39.9
  • Obesity class III: BMI >= 40.0

How This Calculator Works

Enter your weight in kilograms and your height in centimeters. The calculator applies the official WHO formula and returns your BMI with the corresponding classification. It also calculates the ideal weight range for your height, based on the normal range (BMI 18.5-24.9).

When BMI Is Not Enough

BMI is a screening tool, not a diagnosis. It has important limitations:

  • Does not distinguish muscle from fat: a bodybuilder may have a BMI over 30 while being perfectly healthy
  • Does not account for fat distribution: visceral (abdominal) fat is more dangerous than subcutaneous fat
  • Not suitable for children: those under 18 need age- and sex-specific percentile charts
  • Does not consider age and sex: women and older adults naturally have different body compositions

For a more complete assessment, consider supplementing BMI with body fat percentage and waist-to-hip ratio measurements. If your BMI is outside the normal range, consult your doctor for a personalized evaluation.

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Frequently Asked Questions

What is BMI and how is it calculated?▼
BMI (Body Mass Index) is an indicator that relates body weight to height. It is calculated by dividing weight in kilograms by the square of height in meters: BMI = weight / (height squared). It is the international standard recommended by the WHO for classifying weight in adults.
What are the limitations of BMI?▼
BMI does not distinguish between fat mass and lean mass (muscles, bones, water). A muscular athlete could be classified as "overweight" despite having low body fat. It does not consider body fat distribution (visceral vs subcutaneous), age, or sex. For a more complete evaluation, it should be supplemented with body fat measurements or waist-to-hip ratio.
Is BMI valid for children?▼
No. For children and adolescents (ages 2-18), BMI must be interpreted using age- and sex-specific percentile charts, such as those from the CDC or WHO. A BMI of 22 means something very different at age 10 compared to age 30.
What is the ideal BMI for an adult?▼
According to the WHO, the ideal BMI for an adult is between 18.5 and 24.9 (normal weight). Values below 18.5 indicate underweight, 25-29.9 indicate overweight, and 30 or above indicate obesity. However, the optimal value also depends on individual factors such as age, sex, body composition, and overall health status.