BMI Calculator
Calculate BMI (Body Mass Index) by entering your height and weight. Displays obesity classification, standard weight, and normal weight range.
Result
BMI
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| Standard weight (BMI=22) | {{ result.standardWeight }} kg |
| Normal weight range | {{ result.minWeight }} ~ {{ result.maxWeight }} kg |
What BMI calculation is
BMI (Body Mass Index) is an international measure that expresses build from the relationship between weight and height. You find it by dividing weight in kilograms by the square of height in metres: at 170 cm and 65 kg that is 65 ÷ 1.7², about 22.5. The easy mistake is the unit of height — it has to be metres, and calculating with 170 as it stands gives a meaningless figure. This tool accepts centimetres, so you never have to think about the conversion.
The thresholds differ from country to country. This tool follows the criteria of the Japan Society for the Study of Obesity, treating under 18.5 as underweight, 18.5 to under 25 as normal weight, and 25 and above as obese, in four grades. The WHO international standard sets obesity at 30 and above, so bear in mind that the same BMI falls into a wider obese range under the Japanese criteria. BMI uses the same thresholds for men and women, so there is no need to enter a sex.
How BMI is calculated and how to use the tool
- Enter your height in centimetres For 170 cm, type 170. The tool handles the conversion to metres, so the plain figure is fine.
- Enter your weight in kilograms Decimals are accepted, for example 65.4. Using a reading taken after waking and going to the toilet keeps the day-to-day variation small and makes comparison easier.
- Check your BMI, the verdict and the ideal weight Alongside the BMI figure and the obesity verdict, you get the ideal weight corresponding to a BMI of 22 and the weight range counted as normal, equivalent to a BMI of 18.5 to 25.
Tips for getting more out of it
- BMI = Weight (kg) ÷ Height (m)²
- WHO classification: BMI <18.5: Underweight, 18.5–24.9: Normal weight, 25–29.9: Overweight, 30–34.9: Obesity Grade I, 35–39.9: Grade II, ≥40: Grade III.
- Standard weight is derived from BMI=22, which is associated with the lowest disease risk.
- BMI does not account for muscle mass, bone density, or body fat percentage, making it less suitable for athletes with high muscle mass.
When BMI calculation is useful
Making sense of a health check result
You can see which band the BMI figure on your health check sheet falls into. It also serves for grasping the trend by comparing against last year.
Setting a target weight for a diet
Because the normal range is shown in kilograms, a goal such as getting down to a BMI of 24 turns into a concrete figure. The ideal weight at a BMI of 22 is the value statistically associated with the lowest risk of illness.
A rough guide to specific health guidance
Judging metabolic syndrome hinges mainly on waist circumference, but a BMI of 25 or above is the threshold for obesity. It works as a rough guide to whether health guidance is likely to apply.
Looking at the build of children and older people
Bear in mind that this is a measure for adults. Growing children need the obesity index or Kaup index used in schools, and older people need a different view that also weighs the risks of being too thin.
Checking conditions for insurance or blood donation
Where insurance eligibility or the criteria for donating blood include a requirement on build, knowing your BMI in advance makes the process go smoothly.
BMI terms explained
- BMI (Body Mass Index)
- The value obtained by dividing weight in kilograms by the square of height in metres. Because height and weight alone are enough to work it out, it has become a widely used international guide to build.
- Ideal weight
- The weight that brings BMI to 22. It is the value statistically associated with the lowest risk of illness, found by multiplying the square of height in metres by 22.
- Normal weight
- The range where BMI runs from 18.5 to under 25. Under the criteria of the Japan Society for the Study of Obesity, falling inside this range indicates no problem with build.
- Underweight
- The state where BMI is below 18.5. It can go together with poor nutrition and reduced bone density, and calls for as much attention to health as obesity does.
- Obesity (grades 1 to 4)
- The state where BMI is 25 or above, divided into grade 1 from 25 to 30, grade 2 from 30 to 35, grade 3 from 35 to 40, and grade 4 above 40. Grade 3 and above is called severe obesity.
- Japanese criteria
- The thresholds used within Japan. Because they count a BMI of 25 or above as obese, the range classed as obesity is wider than under the WHO international standard, which starts at 30.
- Metabolic syndrome
- The state where, on top of accumulated visceral fat, two or more of blood pressure, blood sugar and lipids exceed their thresholds. The main criterion is waist circumference, so BMI alone cannot establish it.
- Body fat percentage
- The share of body weight made up of fat. Because BMI does not distinguish muscle from fat, this figure has to be looked at as well when assessing the build of someone with a lot of muscle.
FAQ
Note — The Limits of BMI and the "Overweight Paradox"
BMI (Body Mass Index) was devised by Belgian statistician Adolphe Quetelet in the 1830s. It was originally designed for statistical analysis of populations, not for individual health assessment. It was only adopted as a standard for obesity classification in medicine during the latter half of the 20th century.
Epidemiological studies have frequently reported that people with BMI 25–30 (overweight) have the lowest mortality rates — a phenomenon known as the "obesity paradox." This is especially true for the elderly and patients with heart disease, where some extra weight may be associated with better prognosis. This does not mean "being heavier is healthier" — it is evidence that BMI alone cannot fully describe one's health.
For a more accurate body composition assessment, it is important to combine body fat percentage, waist circumference (an indicator of visceral fat), and muscle mass.