BMI Calculator (Body Mass Index)

Calculate your Body Mass Index (BMI) instantly using metric or imperial units. Get your BMI number, category, healthy ranges, and learn how BMI works — including its limitations and alternatives.

What is BMI?

Body Mass Index (BMI) is a simple calculation that compares your weight and height to estimate whether you are underweight, normal weight, overweight, or obese. It is widely used as a screening tool, not a diagnostic tool.

Formulas:

• Metric: BMI = weight (kg) ÷ [height (m)]²
• Imperial: BMI = 703 × weight (lb) ÷ [height (in)]²

BMI Categories (Adults)

These BMI categories apply to most adults aged 18 and older.

These categories may not be accurate for children, athletes, very muscular individuals, or older adults.

Healthy BMI ranges by age (general guidance)

While BMI categories are the same for all adults, body composition naturally changes with age. The ranges below are general population averages, not medical standards.

Healthy BMI by Age (Visual Chart)

Limitations of BMI

BMI is useful for population-level screening, but it has important limitations:

• Does not measure body fat directly — it is based only on height and weight.
• Does not account for muscle mass — athletes may appear “overweight” despite low body fat.
• Does not consider age or sex differences in body composition.
• Does not reflect fat distribution — waist size and where fat is stored also matter.
• Not ideal for children, seniors, or very muscular individuals.

Because of these limitations, BMI should be viewed as a starting point, not a complete picture of health.

Alternatives and complements to BMI

Other measurements can provide a more complete view of health and body composition:

Body fat percentage

Body fat percentage can be estimated using calipers, smart scales, or more advanced methods like DEXA scans. It gives a more direct measure of how much of your body is fat versus lean mass.

Waist-to-height ratio

Waist-to-height ratio is a strong predictor of metabolic and cardiovascular risk. A common guideline is:

Waist-to-height ratio = waist (cm) ÷ height (cm)

Many sources suggest aiming for a value below 0.5.

Waist circumference

Higher waist measurements are associated with increased health risks, even at a “normal” BMI. Common risk thresholds include:

• Men: more than 40 inches (102 cm)
• Women: more than 35 inches (88 cm)

How to improve your BMI safely

If your BMI is outside the normal range, small, sustainable changes can help improve your health over time:

• Focus on a balanced diet with whole foods.
• Include regular physical activity, such as walking, cycling, or swimming.
• Add strength training to build muscle and improve body composition.
• Prioritize sleep and stress management.
• Stay hydrated and avoid excessive sugary drinks.

For personalized advice, always speak with a qualified healthcare professional.

FAQ

Is BMI a perfect measure of health?
No. BMI is a simple screening tool and does not measure body fat, fitness level, or overall health. It should be interpreted alongside other information.

Is BMI accurate for athletes?
Not always. People with high muscle mass may have a higher BMI even if their body fat is low.

Should I rely only on BMI?
No. BMI should not be used as the sole indicator of health. A healthcare professional can provide a more complete assessment.

What is a healthy BMI for adults?
For most adults, a BMI between 18.5 and 24.9 is considered normal.

Can BMI be wrong?
Yes. Because it does not account for muscle, age, sex, or fat distribution, BMI can misclassify some individuals.

Medical disclaimer

This BMI calculator and the information on this page are for general educational purposes only and are not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with any questions about your health, weight, or BMI.