This calculator works out your body mass index from your height and weight, and shows which adult weight category it falls into. It’s for adults aged 20 and older, in metric or US units.
How it’s calculated
Body mass index compares your weight with your height. The calculator uses the standard formulas for adults:
BMI = weight (kg) ÷ height (m)²BMI = 703 × weight (lb) ÷ height (in)²The result is rounded to one decimal place and compared with the adult categories published by the US Centers for Disease Control and Prevention.
Worked example
A person who is 175 cm tall and weighs 70 kg:
- Convert height to meters: 175 cm = 1.75 m.
- Square the height: 1.75 × 1.75 = 3.0625.
- Divide weight by the squared height: 70 ÷ 3.0625 = 22.86.
BMI = 22.9, which is in the healthy weight range.
For the same height, the healthy weight range runs from 18.5 × 3.0625 = 56.7 kg to 24.9 × 3.0625 = 76.3 kg.
BMI categories for adults
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Healthy weight |
| 25.0–29.9 | Overweight |
| 30.0–34.9 | Obesity, class 1 |
| 35.0–39.9 | Obesity, class 2 |
| 40.0 and above | Obesity, class 3 |
These categories apply to adults aged 20 and over, regardless of age, sex or race. Children and teens use BMI-for-age percentiles.
What BMI can’t tell you
BMI is quick and needs no equipment, which makes it useful for screening, but it has limits. It doesn’t measure body fat directly, and it can’t distinguish fat from muscle or bone. It also says nothing about where fat is stored. Use your result as a starting point for a conversation with a healthcare professional, not as a verdict on your health.