BMI Calculator
Calculate your body mass index (BMI) with your weight and height. Indicative; does not replace medical advice.
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BMI is indicative. It does not account for muscle mass or age. Consult a health professional. Need web development? Get a quote.
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Quick demo: how to use this tool
- Enter your weight in kilograms and your height in centimeters.
- Press calculate to see your BMI and the category (underweight, normal, overweight, obese).
- Share the result or try another measurement without reloading the page.
What Body Mass Index is and what it's used for
Body Mass Index (BMI) is the relationship between your weight and height, calculated as BMI = weight (kg) / height (m)². It's the indicator the World Health Organization (WHO) uses as a first-line screening tool to classify adult body weight into five categories: underweight, normal weight, overweight, obesity and severe obesity. BMI doesn't measure body fat directly, but because it's fast, free and needs no special equipment, it remains the most widely used starting reference in medicine, insurance and wellness programs worldwide.
Enter your weight in kilograms and height in centimeters above to get your BMI instantly — no signup, calculated directly in your browser.
BMI interpretation table (WHO)
| Category | BMI (kg/m²) | Associated risk |
|---|---|---|
| Underweight | Below 18.5 | Nutritional risk |
| Normal weight | 18.5 – 24.9 | Low risk (reference range) |
| Overweight | 25.0 – 29.9 | Mild to moderate risk |
| Obesity class I | 30.0 – 34.9 | High risk |
| Obesity class II | 35.0 – 39.9 | Very high risk |
| Obesity class III | 40.0 or more | Extremely high risk |
Source: standard WHO classification for the adult population. These ranges are the same for men and women, though at the same BMI women tend to carry more body fat and men more muscle mass — so BMI is a general guide, not an individual diagnosis.
How to use BMI Calculator
- Enter your weight in kilograms in the corresponding field.
- Enter your height in centimeters (or meters, depending on the form).
- Click Calculate BMI to see your index with the WHO category (underweight, normal, overweight, or obesity).
- Compare your result with the WHO interpretation table above.
Frequently asked questions
What BMI is considered healthy?
A BMI between 18.5 and 24.9 is considered normal weight according to the WHO. Below 18.5 is underweight; between 25 and 29.9 overweight; and over 30, obesity.
Is BMI different for men and women?
The WHO reference ranges are the same for both sexes, but at the same BMI, women tend to have a higher body fat percentage than men, who typically carry more muscle mass. That's why two people with the same BMI can have very different body composition.
Does BMI change with age? What about seniors?
The standard WHO ranges apply to adults aged 18–64. In adults over 65, a slightly higher BMI (up to around 27) is associated with lower risk, since some extra reserve mass can be protective. Under 18, fixed ranges aren't used — age-and-sex percentiles apply instead.
Is BMI useful for athletes and very muscular people?
Not always. BMI doesn't distinguish between fat and muscle, so very muscular people can show as overweight without actually having excess fat. In those cases it's better to measure body fat percentage directly (bioimpedance, skinfold calipers, DEXA scan).
How is BMI calculated?
The weight in kilograms is divided by the height in meters squared (BMI = weight / height²). For example, someone weighing 70 kg (154 lbs) at 1.75 m (5'9") has a BMI of 70 / 1.75² = 22.9 (normal weight). This calculator does it for you instantly.
Is BMI valid for children and pregnant women?
No. In children and teens, WHO growth-curve percentiles by age and sex are used instead, and during pregnancy pre-pregnancy BMI only serves as an initial reference, not a measure during gestation. For children use our child BMI calculator.
What should I do if my BMI shows overweight or obesity?
BMI is a starting point, not a diagnosis. If your result falls outside the normal range, the best next step is to talk to a doctor or dietitian, who can add waist circumference, body composition and your health history before recommending any changes.