Understanding Your BMI (What the Number Means)
BMI estimates whether your weight is healthy for your height. Learn the categories, the formula, and the limits of BMI as a health measure.
BMI (Body Mass Index) is a single number that estimates whether your weight is in a healthy range for your height. It is a quick screening tool, not a diagnosis.
The categories
For most adults:
- Below 18.5 — underweight
- 18.5 to 24.9 — normal weight
- 25 to 29.9 — overweight
- 30 and above — obese
The formula
BMI = weight(kg) ÷ height(m)². In imperial units it is 703 × weight(lb) ÷ height(in)². Both give the same number.
What BMI misses
BMI does not distinguish muscle from fat, or where fat is stored. A muscular athlete can score "overweight" while being very fit, and BMI is less accurate for the elderly, pregnant people and some ethnic groups. Treat it as one signal, alongside waist measurement and how you feel.
Calculate yours
Enter your height and weight in the BMI calculator — metric or imperial, all in your browser. Curious how the percentage math works? See How to calculate a percentage.