BMI calculator — with ideal weight and healthy range
Calculate your Body Mass Index from height and weight, with the classification under either the Japan Society for the Study of Obesity (JASSO) standard or the WHO standard. The result includes the ideal weight (BMI 22), the healthy weight range (BMI 18.5–25), and the difference from the ideal. Toggle the standard with a Mode, and the unit system between metric (cm / kg) and imperial (inch / lb) with an Option. Live computation as you type — everything stays inside your browser.
How to use
1. Pick the classification standard: JASSO (Japan) for use in Japan, WHO for international comparisons. 2. Pick the unit system: metric (cm / kg) or imperial (inch / lb). Switching units clears the numeric inputs — values are not auto-converted, so "70 cm" doesn't become "70 inch". 3. Enter your height and weight; BMI, category, ideal weight, healthy range, and the difference from the ideal update instantly. 4. Use the classification table to see how your BMI compares to the other tiers.
FAQ
- Is my input uploaded?
- No. Everything runs in your browser and is not sent anywhere.
- How do JASSO (Japan) and WHO standards differ?
- Mainly above BMI 25. WHO labels BMI 25–30 as overweight, but JASSO treats the same range as obese class 1. JASSO also adds an obese class 4 tier (≥ 40), so the high end has one more bucket. The underweight / normal range (18.5–25) is identical.
- Why does the ideal weight use BMI 22?
- BMI 22 is statistically associated with the lowest risk of lifestyle-related diseases in adults, and 'ideal weight = (height in m)² × 22' is the widely used formula in Japan.
- My values disappeared when I switched units.
- Intentional. The number 70 means '70 cm' in metric but '70 inch' in imperial — totally different heights — so the inputs are cleared on unit change to avoid silent misreadings.
- What about athletes with high muscle mass?
- BMI uses only height and weight; it does not account for body composition. Athletes and bodybuilders often have a high BMI but a low body-fat percentage, which is not actually obesity. Pair BMI with body-fat or lean-mass measurements for a fuller picture.
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