BMI Calculator

Check your Body Mass Index in seconds

Body Mass Index is one of the quickest ways to see whether your weight sits in a healthy range for your height. This free BMI calculator works it out instantly from your height and weight, supports both metric and imperial units, tells you which category your result falls into, and shows the healthy weight range for your height. It runs entirely in your browser, so your measurements stay private and you get an answer the moment you type.

What BMI actually measures

BMI stands for Body Mass Index, and the formula is simple: your weight in kilograms divided by the square of your height in metres, giving a figure in kg/m². If you prefer pounds, feet and inches, the calculator converts them for you automatically. The number it produces places you into one of four broad bands — underweight, normal, overweight or obese. These bands come from decades of population health research linking body weight to the risk of conditions such as heart disease, high blood pressure and type 2 diabetes.

Understanding the categories

• Under 18.5 — underweight. May indicate insufficient nutrition or an underlying health issue worth discussing with a doctor.
• 18.5 to 24.9 — normal. Associated with the lowest average health risk for most adults.
• 25 to 29.9 — overweight. A signal to pay attention to diet and activity, though not a cause for alarm on its own.
• 30 and above — obese. Linked to higher risk of several chronic conditions and a good reason to seek professional guidance.

Your result is best understood as a starting point for a conversation about your health, not a verdict. Two people with the same BMI can have very different levels of fitness and body composition.

The limitations you should know

BMI is popular because it is cheap and easy, but it has real limitations, and using it wisely means understanding them. Because it relies only on height and weight, it cannot distinguish between muscle and fat, nor tell you where fat is stored. A very muscular athlete may register as "overweight" despite carrying little fat, while an older person who has lost muscle might read as "normal" while carrying more fat than is ideal. BMI also was not designed for children, pregnant people or the very elderly, who need different measures. For a fuller picture, health professionals often combine BMI with waist circumference, body-fat percentage and blood markers.

What to do with your result

If your BMI falls outside the healthy range, the most important step is not to panic but to consider the bigger picture. Sustainable changes — a balanced diet, regular movement, good sleep and managing stress — matter far more than any single number. If you are significantly outside the healthy band, or if you have other risk factors, speak to a doctor or a registered dietitian before making major changes. They can interpret your BMI in the context of your overall health and help you set realistic goals.

How to use the calculator

Choose metric or imperial units, then enter your height and weight. Your BMI, its category and the healthy weight range for your height appear instantly. Because it works locally, you can recalculate as often as you like — for example to see how reaching a target weight would change your result. Used sensibly, and alongside professional advice when needed, BMI is a handy way to keep an eye on one aspect of your long-term health.

Beyond BMI: other measures worth knowing

Because BMI only uses height and weight, health professionals often pair it with other simple measures for a fuller picture. Waist circumference is one of the most useful, because fat stored around the abdomen carries more health risk than fat on the hips and thighs; a large waist can flag risk even when BMI looks normal. The related waist-to-height ratio — keeping your waist under half your height — is an easy rule of thumb that many researchers consider a better predictor of risk than BMI alone. Body-fat percentage, measured with calipers or specialised scales, distinguishes muscle from fat directly, which BMI cannot do. And for a rounded view of health, none of these numbers matter as much as habits: regular physical activity, a balanced diet rich in whole foods, adequate sleep and not smoking influence long-term outcomes far more than any single measurement. Treat BMI as one quick indicator among several, use it to spot trends over time rather than to judge a single day, and always interpret it alongside how you actually feel and what a professional advises.

How is BMI calculated?

BMI is your weight in kilograms divided by the square of your height in metres. The tool does the conversion for you whether you enter metric or imperial units.

What is a healthy BMI range?

For most adults a BMI between 18.5 and 24.9 is considered healthy. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is in the obese range.

Is BMI accurate for everyone?

BMI is a useful general screen but it does not measure body fat directly. Very muscular people may read high despite low fat, so treat it as a guide, not a diagnosis.

Does it work with pounds and feet?

Yes. Switch to imperial mode to enter height in feet and inches and weight in pounds, and the healthy weight range is shown back in the same units.