BMI Calculator
BMI (Body Mass Index) is a quick screening tool to assess whether your weight falls within a healthy range for your height. Free and instant.
Built and reviewed by Jesse · Last reviewed
Fill in your details to see your BMI.
- Enter your height. In centimeters, or feet and inches.
- Enter your weight. In kilograms or pounds.
- Read your BMI and category. The result places you in the WHO weight category for adults.
BMI is calculated using a simple formula:
BMI = weight (kg) / [height (m)]²
For example, if you weigh 70 kg and are 1.75 m tall (175 cm), your BMI is 70 / (1.75 × 1.75) = 22.9, which falls in the "normal weight" category.
Want a goal weight instead? The ideal weight calculator works in reverse to show a healthy weight range for your height.
The World Health Organization classifies adult BMI as follows:
| Category | BMI range (kg/m²) | Notes |
|---|---|---|
| Underweight | Below 18.5 | May indicate malnutrition or underlying health issues. |
| Normal weight | 18.5–24.9 | Lowest health risk in population studies. |
| Overweight | 25.0–29.9 | Elevated risk of metabolic disease. |
| Obese | 30.0 and above | Higher risk of chronic disease; medical guidance advised. |
BMI is a useful screening tool, but it has important limitations:
- Doesn't measure body fat. BMI treats all weight equally. Two people with the same BMI can have very different body compositions — one might be muscular, the other high body fat. A body fat calculator gives a clearer picture.
- Not suitable for athletes.People with high muscle mass often have "overweight" or "obese" BMI despite being healthy and fit.
- Ignores fat distribution.Belly fat (visceral fat) is more harmful than fat stored elsewhere, but BMI doesn't account for this. Waist circumference is a better predictor of metabolic risk.
- Population averages. BMI cutoffs are based on population studies, not individuals. Your health risk depends on many factors beyond BMI: genetics, diet, activity, sleep, stress, and more.
BMI is best used as a quick health screening tool for the general population. It can help identify whether further assessment is needed, but it should not be the only metric you rely on. For a fuller picture, combine BMI with waist circumference, body fat percentage, blood markers (cholesterol, glucose), and how you feel physically.
If your BMI is outside the normal range and you're unsure what to do, consult a doctor or registered dietitian. They can assess your overall health and recommend personalized next steps.
Body Mass Index
BMI = weight(kg) / height(m)^2- weight
- = body weight in kilograms
- height
- = height in meters
WHO adult categories: under 18.5 = underweight, 18.5-24.9 = normal, 25.0-29.9 = overweight, 30.0 and above = obese.
What is BMI?
BMI (Body Mass Index) is a simple calculation using your height and weight (BMI = kg/m²). It's used as a screening tool to categorize whether someone is underweight, normal weight, overweight, or obese.
How accurate is BMI?
BMI is a quick population-level screening tool, but it has limitations. It doesn't distinguish between muscle and fat, so athletes or very muscular people may be categorized as overweight despite being healthy. It also doesn't account for age, sex, or body composition. Use it as a starting point, not a definitive health assessment.
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered normal weight. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is classified as obese. These ranges are based on population studies linking BMI to health risk.
Does BMI apply to everyone?
No. BMI is not suitable for children, pregnant women, elderly adults, or highly trained athletes. It's designed for the general adult population. If you have significant muscle mass or a medical condition, consult a healthcare provider instead of relying on BMI alone.
Why does BMI matter?
Higher BMI is statistically associated with increased risk of type 2 diabetes, heart disease, high blood pressure, and certain cancers. Lower BMI (underweight) is associated with nutrient deficiencies and weakened immunity. BMI helps identify risk, but it's not a direct measure of health.
What if my BMI is too high or too low?
If your BMI is outside the normal range, consider lifestyle changes (diet, exercise) and consult a doctor or registered dietitian. Small, sustainable changes are more effective than extreme diets. BMI is a signal to investigate further, not a diagnosis.
Can I have a high BMI but still be healthy?
Yes. If you carry significant muscle mass (e.g., from strength training), your BMI may categorize you as overweight even though your body fat is low. In this case, other metrics like body fat percentage, waist circumference, or metabolic health markers are more informative than BMI alone.
References
FitCalcs calculators provide general estimates for healthy adults and are not medical advice.
Related calculators
Ideal Weight Calculator
Find a realistic goal weight for your height using classic formulas and your healthy BMI range.
Body Fat Calculator
Estimate your body fat percentage with just a tape measure using the U.S. Navy method.
TDEE Calculator
Calculate your Total Daily Energy Expenditure (TDEE) and find out how many calories you burn per day.