What is BMI?
Body Mass Index (BMI) is a simple screening number that estimates whether your weight is in a healthy range for your height. It's calculated from weight and height alone, which makes it quick but also means it's a rough guide rather than a precise health measure.
The formula
BMI = weight (kg) ÷ height (m)²
Example: someone weighing 70 kg and 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. In pounds and inches: weight (lb) ÷ height (in)² × 703.
BMI categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
Limits of BMI
BMI does not account for muscle, bone density, age, sex, or fat distribution, so muscular people can score high without being overweight. It also doesn't apply to children, teenagers, or pregnant people.
Frequently asked questions
Is BMI accurate?
BMI is a quick screening tool, not a diagnosis. It can misclassify very muscular or very lean people because it can't distinguish muscle from fat.
What is a healthy BMI?
For most adults, 18.5–24.9 is considered healthy, though the ideal varies with age, ethnicity, and body composition.
Does BMI work the same for men and women?
The adult BMI ranges are the same, but at the same BMI women tend to carry more body fat than men.
Is my data saved?
No. Everything runs in your browser and nothing you type is sent to a server.
Not medical advice. Talk to a healthcare professional about your individual health.