How to use
- Choose "Metric (cm, kg)" or "US units (ft, in, lb)".
- Enter your height and weight. For US units, enter feet as a whole number and inches as a number less than 12.
- Enter your age if you like, then select "Calculate". Your BMI, category, and weight range appear below.
The BMI formula
BMI = weight (kg) / height (m) squared. For example, at 170 cm and 65 kg, BMI is 65 / (1.7 × 1.7), which rounds to 22.5.
US inputs use these exact conversions: 1 in = 2.54 cm and 1 lb = 0.45359237 kg. The category is determined before rounding the displayed BMI.
Adult BMI categories
This tool uses standard adult BMI categories (WHO cutoffs, also used by the CDC). The intervals below refer to the unrounded BMI; a value that displays as 25.0 but is actually below 25 (for example, 24.96) is still classified as normal weight.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to below 25 | Normal weight |
| 25 to below 30 | Overweight |
| 30 to below 35 | Obesity class I |
| 35 to below 40 | Obesity class II |
| 40 or higher | Obesity class III |
Weight range and limitations
The weight range is your height in meters, squared, multiplied by 18.5 and by 25, with the upper limit excluded. At 170 cm, that works out to about 53.4 to less than 72.3 kg. These are approximate figures, not personal target weights, with the lower limit rounded down and the upper limit rounded up to one decimal place.
BMI does not distinguish muscle from fat, and it is not a diagnosis. These categories apply to adults age 20 and over. Children and teenagers under 20 need BMI-for-age comparisons based on age and sex. If you are pregnant, ask a health professional how to interpret BMI. This calculator accepts heights from 100 to 250 cm and weights from 20 to 300 kg, or their US equivalents.
Sources and specifications
Adult classification: World Health Organization (Technical Report Series 894, 2000) and CDC adult BMI categories. Unit definitions: NIST Handbook 44, Appendix C (international inch and international avoirdupois pound). The weight range is simply calculated from BMI 18.5 to less than 25. It is not a separate medical recommendation.
Frequently asked questions
How is BMI calculated?
BMI is weight in kilograms divided by height in meters squared. US inputs are converted using 1 in = 2.54 cm and 1 lb = 0.45359237 kg.
Which categories does this calculator use?
It uses the standard adult BMI categories (WHO cutoffs, also used by the CDC): underweight below 18.5, normal weight from 18.5 to below 25, overweight from 25 to below 30, and obesity at 30 or higher. Obesity classes I, II, and III begin at 30, 35, and 40.
Why does a BMI of 25.0 show as normal weight?
The display rounds BMI to one decimal place, but the category uses the unrounded value. For example, 24.96 displays as 25.0 and remains below the overweight cutoff.
Is the weight range my target weight?
No. It is the weight range calculated from BMI 18.5 to less than 25 at your height, with rounded figures. It is not an individual recommendation.
Can children or pregnant people use it?
These categories apply to adults age 20 and over. Children and teenagers under 20 need BMI-for-age comparisons based on age and sex. If you are pregnant, ask a health professional how to interpret BMI. If you enter an age under 20, the calculator will not show a result. BMI alone is not a diagnosis.