BMI Calculator (Body Mass Index)
Enter your weight and height — in metric or US units — and get your result instantly, with your range and personalized recommendations.
Enter your weight and height to see your result.
The healthy BMI range according to the WHO is 18.5 to 24.9.
🔒 Your weight and height are calculated on your own device — never sent to or stored on any server.
How it works
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Enter your details
Type your weight and height above, in metric (kg, cm) or US units (lb, ft/in) — whichever you prefer.
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Instant calculation
We apply the official BMI formula (weight ÷ height²) as soon as you complete both fields.
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Result and recommendations
See your BMI, which range you fall into, and guidance based on your result.
What is Body Mass Index?
Body Mass Index (BMI) is a value that relates a person's body weight to their height. It has been used for decades as a quick, simple first reference to estimate whether an adult's weight falls within a range considered healthy, or whether it's below (underweight) or above (overweight or obesity) that range.
The formula dates back to the 19th century and Belgian mathematician Adolphe Quetelet, and today the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC) both use it as the standard population-level reference for classifying adult body weight.
How BMI is calculated
The formula is simple: divide weight in kilograms by height in meters, squared.
BMI = weight (kg) ÷ [height (m)]²
For example, a person who weighs 68 kg (about 150 lb) and is 1.68 m (about 5'6") tall would have a BMI of 68 ÷ (1.68 × 1.68) = 24.1, within the range considered normal.
Why it's useful to know your BMI
Knowing your BMI gives you a quick snapshot of your weight relative to your height, and it's one of the indicators healthcare professionals use — alongside other data — as a starting point to assess a person's general status. It doesn't replace a medical visit, but it can help you identify whether it's worth paying closer attention to your habits or consulting a specialist.
Limitations of BMI
BMI is useful at a population level, but it has well-known limits at the individual level: it doesn't distinguish between muscle mass and fat mass (so it can overestimate the result in athletes or very muscular people), it doesn't account for where fat is distributed in the body, and it may not accurately reflect body composition in older adults, pregnant or breastfeeding women, or people with an atypical build. For that reason, this calculator's result should be read as a general reference, not a medical diagnosis.
BMI range table (WHO / CDC)
| BMI (kg/m²) | Category |
|---|---|
| Below 16.0 | Severe thinness |
| 16.0 – 16.9 | Moderate thinness |
| 17.0 – 18.4 | Mild thinness (underweight) |
| 18.5 – 24.9 | Normal / healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity class I |
| 35.0 – 39.9 | Obesity class II |
| 40.0 or more | Obesity class III (severe) |
Reference classification from the World Health Organization for adults; the CDC uses the same cutoffs for U.S. adults. It doesn't apply in the same way to minors, high-performance athletes, or pregnant women.
Source: World Health Organization (WHO) — "Obesity and overweight", who.int, and CDC — "Adult BMI Categories", cdc.gov.
Frequently asked questions about BMI
What is BMI (Body Mass Index)?
BMI is a measure that relates your weight to your height to estimate whether you're within a healthy weight range. It's calculated by dividing weight in kilograms by height in meters squared (kg/m²). It's a quick reference tool, not a medical diagnosis.
How is BMI calculated?
The formula is BMI = weight (kg) ÷ height (m)². For example, someone weighing 70 kg (about 154 lb) and 1.75 m (about 5'9") tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, within the normal range.
What BMI range is considered normal or healthy?
According to the World Health Organization (WHO) and the CDC, the normal (healthy weight) range for adults is between 18.5 and 24.9. Below that is considered underweight, and above it, overweight or obesity.
Is BMI accurate for everyone?
Not exactly. BMI doesn't distinguish between muscle mass and fat mass, so it can overestimate the result for very muscular people, and it may not accurately reflect body composition in older adults, pregnant women, or people with low muscle mass. It's a general guide, not an individual diagnosis.
My BMI shows overweight or obesity — what should I do?
A high BMI is a signal to pay attention to your habits, but the best way to interpret the result is together with a healthcare professional, who can assess other factors like body composition and your medical history. A balanced diet and regular physical activity are usually a good starting point.
Does BMI work for children and teenagers?
Not in the same way. For people under 20, BMI-for-age percentile charts by sex are used instead, which differ from the adult scale. This calculator is designed for adults.
How often should I calculate my BMI?
There's no fixed rule; many people check it every few months as a general reference within a broader health routine, not as a daily measurement.
Does a low or high BMI mean I have a health problem?
Not necessarily. BMI is just a statistical indicator. A value outside the normal range doesn't automatically mean disease, just as being within range doesn't guarantee good health. For a real assessment, consult a healthcare professional.
This calculator is for informational and educational purposes only. It does not replace the diagnosis, advice, or treatment of a qualified medical professional. If you have any concerns about your weight or health, please consult your doctor or a registered dietitian.