BMI Calculator

Enter your height and weight to instantly calculate your Body Mass Index (BMI) and check your classification as underweight, normal, overweight, or obese, plus your healthy weight range.

Classification Standard

How to Use

  1. Enter height

    Input your height in centimeters (cm) or feet and inches.

  2. Enter weight

    Input your current weight in kilograms (kg) or pounds (lbs).

  3. View results

    Click calculate to see your BMI value and weight category classification.

What is BMI (Body Mass Index)?

BMI (Body Mass Index) is an index devised in the 1830s by the Belgian statistician Adolphe Quetelet. It expresses the degree of obesity as a single number by dividing weight by height squared. Because it can be calculated from just height and weight, it is the most widely used first-line tool for screening obesity in clinical settings and health check-ups.

BMI does not directly measure body fat, but at the population level it correlates fairly strongly with body fat percentage and the risk of chronic conditions such as cardiovascular disease and diabetes. For this reason, both the World Health Organization (WHO) and the Korean Society for the Study of Obesity have adopted BMI as an official criterion for diagnosing obesity.

However, the same height and weight may be classified as 'normal' under one standard and 'overweight' under another, so it is important to choose and interpret the criterion that suits you.

Calculation Formula

BMI is calculated with the following formula.

BMI = weight (kg) ÷ height (m)²

Note that height is measured in metres, not centimetres. For example, a person who is 170 cm tall and weighs 68 kg would calculate it as follows.

  • Convert height to metres: 170 cm = 1.70 m
  • Square the height: 1.70 × 1.70 = 2.89
  • BMI: 68 ÷ 2.89 ≈ 23.5

This value of 23.5 is normal (18.5–24.9) under the WHO standard, but corresponds to pre-obese (23–24.9) under the Korean Society for the Study of Obesity standard.

Frequently Asked Questions

What is BMI?
BMI (Body Mass Index) is your weight in kilograms divided by the square of your height in metres, and it is the most widely used index for assessing obesity. It is used as a diagnostic criterion for obesity by the World Health Organization (WHO) and the Korean Society for the Study of Obesity.
What is the normal BMI range?
Under the WHO international standard, a BMI of 18.5–24.9 is the normal range. Under the Korean Society for the Study of Obesity (Asia-Pacific) standard, 18.5–22.9 is normal, and 23 or above is classified as pre-obese (overweight). Asians tend to have a higher body fat percentage at the same BMI, so a stricter standard is applied.
Are the BMI standards different for Asians and Westerners?
Yes. Asians face a higher risk of abdominal obesity and metabolic disease at the same BMI, so the Korean Society for the Study of Obesity classifies a BMI of 23 as overweight and 25 as obese. This is stricter than the WHO standard (25 for overweight, 30 for obese).
What are the limitations of BMI?
BMI does not reflect muscle mass, frame size, or fat distribution. An athlete with high muscle mass may have a high BMI yet be healthy, while a person with a normal BMI may still have abdominal obesity. For a more accurate assessment of obesity, it is recommended to also check body fat percentage, waist circumference, and similar measures.
What is the difference between BMI and body fat percentage?
BMI is an indirect index calculated from height and weight alone, whereas body fat percentage directly measures the proportion of body weight that is fat. Body fat percentage is more accurate but harder to measure, while BMI offers a simple way to estimate obesity, so it is widely used as a first-line screening tool.
How can I find the healthy weight for my height?
Multiply the normal BMI range by the square of your height (m²) to obtain your healthy weight range. For example, at a height of 165 cm (1.65 m), the WHO standard gives 18.5×2.72 ≈ 50.4 kg to 24.9×2.72 ≈ 67.8 kg as the healthy weight range. You can check the value for your height directly in the calculator's 'Healthy Weight Range' result.
Do the same BMI standards apply to children and older adults?
No. Adult BMI standards apply only to adults aged 18 and over. Children and adolescents change as they grow, so age- and sex-specific BMI percentiles (growth charts) are used, and in older adults BMI may appear lower than reality due to muscle loss, so a comprehensive assessment is needed rather than BMI alone.
Updated 2026 — WHO standards

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