BMI Calculator
Calculate your BMI (body mass index) and healthy (standard) weight from your height and weight. Shows both the WHO (international) classification and Japan's JASSO classification. Everything runs in your browser — your height and weight are never sent anywhere. This is not medical advice; use it as a general guide only.
The height and weight you enter are processed entirely in your browser and are never sent anywhere.
This tool is not medical advice. Please consult a medical professional for decisions about your health. It may not apply if you're pregnant, still growing, or have an unusually high muscle mass.
Enter your height and weight, then select Calculate.
- BMI
- Category (WHO standard)
- Standard (healthy) weight
- Difference from standard weight
For reference, under Japan's JASSO standard:
How to use
- Enter your height (cm) and weight (kg).
- Select Calculate.
- See your BMI, category under both the WHO and JASSO standards, and your standard (healthy) weight.
How it works
The BMI formula
BMI = weight (kg) ÷ height (m)^2
The BMI value shown is rounded to one decimal place, but the category (underweight, normal, obese, etc.) is decided using the unrounded value. So a displayed value of "25.0" that's actually 24.97 underneath will still be classified as "Normal weight".
Classification: WHO vs. Japan (JASSO)
The cutoffs — 18.5, 25.0, 30.0, 35.0, and 40.0 — are the same under both standards. What differs is the label. In particular, the BMI 25–30 range is already called "Obesity (level 1)" under Japan's JASSO standard, while the WHO (international) standard calls the same range "Overweight" — not yet "Obese".
- Below BMI 18.5: WHO "Underweight" / Japan (JASSO) "Underweight"
- BMI 18.5 to below 25.0: WHO "Normal weight" / Japan (JASSO) "Normal weight"
- BMI 25.0 to below 30.0: WHO "Overweight" / Japan (JASSO) "Obesity (level 1)"
- BMI 30.0 to below 35.0: WHO "Obese Class I" / Japan (JASSO) "Obesity (level 2)"
- BMI 35.0 to below 40.0: WHO "Obese Class II" / Japan (JASSO) "Obesity (level 3)"
- BMI 40.0 and above: WHO "Obese Class III" / Japan (JASSO) "Obesity (level 4)"
Source: Japan's Ministry of Health, Labour and Welfare (e-Health Net), "Obesity and Health"; CDC Adult BMI Categories.
The standard (healthy) weight formula
standard weight (kg) = height (m)^2 × 22
A BMI of 22.0 is the value Japan's e-Health Net identifies as statistically associated with the lowest risk of diabetes, hypertension, and dyslipidemia — the conditions most strongly linked to obesity.
When this doesn't apply well
BMI is a simple measure based only on height and weight — it doesn't account for body fat percentage or muscle mass. Athletes with high muscle mass can score a high BMI without being overweight in any meaningful sense. It also doesn't apply directly if you're pregnant or still growing. Talk to a medical professional for decisions about your health.
FAQ
Is my height and weight sent anywhere?
No. The calculation happens entirely in your browser, with no connection to any external server.
Is a BMI of 25 considered obese?
It depends which standard you use. Under Japan's JASSO standard, BMI 25 and above is already classified as "Obesity (level 1)". Under the WHO (international) standard, BMI 25–30 is "Overweight", and the word "Obese" is only used from BMI 30 upward. So the same BMI of 27 is called "obese" under the Japanese standard but "overweight" under WHO's — the underlying cutoff numbers (25, 30, etc.) are identical between the two, only the labels differ.
What does "standard weight" mean?
It's the weight corresponding to a BMI of 22.0, the value statistically associated with the lowest risk of several major diseases. It isn't a target you're required to hit — treat it as a general reference point.
Does this apply to athletes or people with a lot of muscle?
Not reliably. BMI only looks at height and weight, so it can't distinguish muscle from fat. Someone with high muscle mass can score a high BMI without carrying excess body fat.
Can I use this while pregnant or for a child?
No. This tool is intended as a general guide for adults. Pregnancy and childhood growth need different reference standards, so please consult a medical professional instead.
Related tools
- Japanese Age, School Grade & Zodiac CalculatorCalculate age, Japanese school grade and Chinese/Japanese zodiac from a date of birth. This tool follows Japan's specific school-year cutoff (April 2) and the Japanese legal age-counting rule, so it's tailored to Japanese conventions rather than a generic age calculator. Everything runs in your browser — nothing is ever sent anywhere.
- Anniversary & Days Elapsed CalculatorCalculate how many days it's been since a start date — like the day you started dating, a wedding anniversary, or a birthday — and find upcoming milestones like the 100th day, 1000th day, or Nth anniversary. You can also work out what date is N days or N years from a start date. Everything runs in your browser, so the dates you enter are never sent anywhere.
- Japanese Business Day CalculatorWork out business days in Japan with weekends and public holidays excluded — including substitute holidays. Find the date N business days out, or count the business days in a range. Everything runs in your browser; your dates are never sent anywhere.
- Japan Child & Childcare Support Levy Calculator (April 2026) | Monthly estimate by insurerEstimate your monthly and annual burden under Japan's new Child and Childcare Support Levy (starting April 2026), based on your health insurer type (Kyokai Kenpo, company health insurance union, mutual aid association, National Health Insurance, or the elderly medical system) and annual income, using figures published by the Children and Families Agency. Also see the projected FY2026-FY2028 system-wide average trend. Your income is processed entirely in your browser and never sent anywhere.
- All tools