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BMI Calculator for Adults
Enter your height and weight to see your Body Mass Index, your category under both WHO and Asian cut-offs, and the weight range that matches a healthy BMI for your height.
What BMI is, in plain terms
Body Mass Index compares your weight with your height. It was designed for studying populations, and it remains a quick first screen because it needs only a scale and a tape measure. It does not measure body fat directly. Two people with the same BMI can have very different amounts of muscle and fat.
Formula and categories
BMI = weight (kg) ÷ height (m)² or, in imperial units, BMI = 703 × weight (lb) ÷ height (in)².
Worked example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9.
| BMI (kg/m²) | WHO category |
|---|---|
| Below 16 | Severe thinness |
| 16 to 16.9 | Moderate thinness |
| 17 to 18.4 | Mild thinness |
| 18.5 to 24.9 | Normal range |
| 25 to 29.9 | Overweight |
| 30 to 34.9 | Obesity class I |
| 35 to 39.9 | Obesity class II |
| 40 and above | Obesity class III |
Why we also show Asian cut-offs
A WHO expert consultation found that many Asian populations carry more body fat and higher risk of type 2 diabetes and heart disease at lower BMI values than the standard cut-offs imply. It proposed public-health action points at 23 and 27.5. Some countries publish their own variations, so treat these as screening thresholds and ask your clinician which ones they use.
| BMI | Asian public-health category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 22.9 | Normal range |
| 23 to 27.4 | Increased risk |
| 27.5 and above | High risk |
Waist-to-height ratio: the missing second number
Where fat sits matters. Divide your waist by your height (same units). A result of 0.5 or above suggests extra central fat, a pattern linked with metabolic risk, even when BMI looks normal. The simple version is: keep your waist below half your height. Measure at the navel, relaxed, after breathing out.
Limits of BMI
- Muscle: strength athletes can read as overweight with low body fat.
- Age: older adults tend to carry more fat at the same BMI and can lose muscle without losing weight.
- Ethnicity: risk thresholds differ, as above.
- Pregnancy: standard BMI does not apply.
- Single number: blood pressure, blood sugar, lipids and fitness tell you more about health than BMI does.
What to do with your result
- Note your category and your healthy range, but treat them as a screen, not a verdict.
- Measure your waist and check the ratio.
- Estimate composition with the body fat calculator.
- If you want to change weight, set a realistic daily target with the calorie calculator.
- If your BMI is below 18.5, or in a higher-risk range, book a check-up for blood pressure, glucose and cholesterol.
Medical disclaimer: This tool is for education and general planning. It is not medical advice and does not diagnose any condition. If you are pregnant, under 18, have an eating-disorder history or a medical condition, speak to a doctor or registered dietitian before changing your diet or exercise.
Frequently asked questions
What is a healthy BMI?
The WHO normal range is 18.5 to 24.9. Using Asian public-health cut-offs the normal range is 18.5 to 22.9.
Is BMI accurate for athletes?
Not reliably. It cannot tell muscle from fat, so athletes should look at body fat, waist measurements and performance instead.
Can I use this BMI calculator for my child?
No. Children and teens are assessed with BMI-for-age percentiles on CDC or WHO growth charts, not adult cut-offs.
What is BMI Prime?
It is your BMI divided by 25, the upper limit of the WHO normal range. A value above 1 means your BMI is above 25.
How often should I check my BMI?
Monthly is plenty. Day-to-day weight swings of 1 to 2 kg are normal water changes.