BMI & Ideal Weight Calculator
＋More features: target weight from a target BMI, weight reference table
Target weight from a target BMI
Enter the BMI you are aiming for, and this calculates the target weight and how many kg to go (using the height and weight above).
Weight reference table for your height
Lists the weights for BMI 18.5–30 at the height entered above.
Enter your height and weight to instantly get your BMI and ideal weight, judged by the Japanese standard used in health checkups in Japan (from “underweight” to “obese”). Useful for reading your Japanese health-checkup results or setting a weight goal.
How to use
- Enter your height in centimeters (e.g. 170).
- Enter your weight in kilograms (e.g. 60).
- Your BMI, its category and your ideal weight appear below as you type — no button needed.
How it is calculated
This tool uses the following formulas (BMI is shown to one decimal place, and the category is judged on the displayed value).
- BMI = weight (kg) ÷ height (m) ÷ height (m)
- Ideal weight = 22 × height (m) × height (m)
A BMI of 22 is statistically associated with the lowest risk of disease, and the weight at BMI 22 is called the “ideal weight” (標準体重) in Japan.
Categories follow the standard for adults of the Japanese Society for the Study of Obesity (JASSO).
| BMI | Category |
|---|---|
| Under 18.5 | Underweight |
| 18.5 to under 25 | Normal weight |
| 25 to under 30 | Obese (class 1) |
| 30 to under 35 | Obese (class 2) |
| 35 to under 40 | Obese (class 3) |
| 40 and over | Obese (class 4) |
Sources (primary information)
- Ministry of Health, Labour and Welfare (Japan), e-Health Net “BMI” — formula and the BMI 22 baseline, in Japanese
https://kennet.mhlw.go.jp/information/information/dictionary/metabolic/ym-002.html (accessed July 26, 2026) - Japanese Society for the Study of Obesity, “Guidelines for the Management of Obesity Disease 2016” — BMI categories, in Japanese
JASSO official site (accessed July 26, 2026)
Assumptions and notes
- For adults only. Children are assessed with growth charts and other age-specific indexes, and BMI does not apply during pregnancy.
- BMI is calculated from height and weight only, so it does not reflect muscle mass or body-fat percentage. Muscular people may get a high BMI.
- The categories are the Japanese standard. Under the WHO international standard, “obese” starts at BMI 30 — so a checkup in Japan may call you “obese (class 1)” at a BMI that the WHO standard calls “overweight”.
Frequently asked questions
My BMI is “normal weight” but I am unhappy with my body shape.
BMI uses only height and weight and cannot tell muscle from fat. For body composition (body-fat percentage, muscle mass), use a body-composition scale or a professional measurement.
Can I use this for my child?
No. Children are assessed with growth charts and age-specific indexes such as the Rohrer index. Follow the assessment of the school or pediatrician.
Should everyone aim for the ideal weight (BMI 22)?
BMI 22 is the value statistically associated with the fewest diseases — it is not a goal everyone must reach. The right weight depends on your age and health; consult a doctor.