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Calculate your Body Mass Index instantly using metric (kg/m) or imperial (lbs/ft) units. Switch between unit systems, view your BMI category, and learn what your score means for your health.
Your BMI
22.86
Normal weight
The World Health Organization classifies BMI into the following categories. These ranges apply to adults aged 20 and older.
| Category | BMI Range | Health Risk |
|---|---|---|
| Severe Thinness | < 16.0 | Very High |
| Moderate Thinness | 16.0 – 16.9 | High |
| Mild Thinness | 17.0 – 18.4 | Moderate |
| Normal Weight | 18.5 – 24.9 | Low |
| Overweight (Pre-obese) | 25.0 – 29.9 | Increased |
| Obese Class I | 30.0 – 34.9 | High |
| Obese Class II | 35.0 – 39.9 | Very High |
| Obese Class III | ≥ 40.0 | Extremely High |
Body Mass Index, commonly abbreviated as BMI, is a numerical value derived from a person's weight and height. It provides a simple, inexpensive screening method that categorizes individuals into weight groups ranging from underweight to obese. BMI was originally developed by Belgian mathematician and statistician Adolphe Quetelet between 1830 and 1850 as part of his work on “social physics,” and the formula has remained essentially unchanged ever since.
The calculation produces a single number measured in kg/m², although in everyday use the units are often omitted. Public health organizations including the World Health Organization (WHO), the National Institutes of Health (NIH), and the Centers for Disease Control and Prevention (CDC) all use BMI as a population-level screening tool to identify potential weight-related health risks.
It is important to understand that BMI is a screening metric, not a diagnostic tool. It cannot measure body fat directly, nor does it account for factors such as muscle mass, bone density, age, sex, or ethnic differences in body composition. Two people with identical BMI values can have very different body fat percentages. For this reason, healthcare providers use BMI alongside other assessments such as waist circumference, skin-fold measurements, and blood tests to form a complete picture of a patient's health.
Despite its limitations, BMI remains widely used because of its simplicity and strong statistical correlation with body fat levels across large populations. Converting between metric and imperial measurement systems is straightforward, and this calculator handles both seamlessly.
BMI = weight (kg) ÷ height (m)²
Divide your weight in kilograms by the square of your height in meters. For example, if you weigh 70 kg and stand 1.75 m tall, square 1.75 to get 3.0625, then divide 70 by 3.0625 to get a BMI of 22.86.
BMI = (weight (lbs) ÷ height (in)²) × 703
First convert your height entirely to inches (feet × 12 + remaining inches). Divide your weight in pounds by the square of your total height in inches, then multiply the result by 703. The constant 703 bridges the unit gap between the metric and imperial systems so both formulas yield the same BMI value.
For a quick metric estimate, multiply your height in meters by itself, then see how many times that number fits into your weight. If you are roughly 1.7 m tall, 1.7 × 1.7 ≈ 2.9. A weight of 72 kg divided by 2.9 gives approximately 24.8 — right at the upper edge of normal weight. This quick mental check can help you gauge your BMI without a calculator.
| Weight (kg) | 1.55 m | 1.65 m | 1.75 m | 1.85 m | 1.95 m |
|---|---|---|---|---|---|
| 50 | 20.8 | 18.4 | 16.3 | 14.6 | 13.1 |
| 60 | 25.0 | 22.0 | 19.6 | 17.5 | 15.8 |
| 70 | 29.1 | 25.7 | 22.9 | 20.5 | 18.4 |
| 80 | 33.3 | 29.4 | 26.1 | 23.4 | 21.0 |
| 90 | 37.5 | 33.1 | 29.4 | 26.3 | 23.7 |
| 100 | 41.6 | 36.7 | 32.7 | 29.2 | 26.3 |
| Weight (lbs) | 5′2″ | 5′6″ | 5′10″ | 6′0″ | 6′4″ |
|---|---|---|---|---|---|
| 120 | 21.9 | 19.4 | 17.2 | 16.3 | 14.6 |
| 140 | 25.6 | 22.6 | 20.1 | 19.0 | 17.0 |
| 160 | 29.3 | 25.8 | 23.0 | 21.7 | 19.5 |
| 180 | 32.9 | 29.1 | 25.8 | 24.4 | 21.9 |
| 200 | 36.6 | 32.3 | 28.7 | 27.1 | 24.4 |
| 220 | 40.3 | 35.5 | 31.6 | 29.8 | 26.8 |
Values rounded to one decimal place. Use the calculator above for precise results.
BMI provides a fast initial assessment of weight-related health risk. A single number can indicate whether further evaluation is warranted.
Monitoring your BMI over time helps track the effectiveness of diet and exercise programs. A trending change is more meaningful than a single measurement.
Epidemiologists and public health researchers use BMI data to study obesity trends across demographics, regions, and time periods at population scale.
Many clinical guidelines and insurance policies reference BMI thresholds for eligibility for surgical interventions, medications, or nutritional counseling programs.
Weigh yourself in the morning before eating for the most consistent readings. Daily fluctuations of 1-2 kg (2-4 lbs) from water and food are normal.
Mixing unit systems. A common error is entering weight in pounds but height in meters. Always ensure both measurements use the same system (both metric or both imperial).
Measure height without shoes and stand against a flat wall for accuracy. Even 1-2 cm of error can shift your BMI by 0.3-0.5 points.
Entering height in centimeters instead of meters in the metric formula. If your height is 175 cm, you must enter 1.75 m. Using 175 directly produces an absurdly small BMI.
Use BMI as one data point among many. Combine it with waist circumference, body fat percentage, and blood work for a fuller health picture.
Forgetting that the imperial formula requires total height in inches, not a combination of feet and inches. Convert feet to inches first (5 ft 9 in = 69 inches), then square the total.
BMI is calculated by dividing your weight in kilograms by the square of your height in meters: BMI = weight (kg) / height (m)². For imperial units, the formula is BMI = (weight in pounds / height in inches²) × 703.
BMI has limitations. It does not distinguish between muscle and fat mass, and may not be accurate for athletes, elderly individuals, or pregnant women. People with high muscle mass may have a high BMI without excess body fat. Always consult healthcare professionals for a comprehensive assessment.
A BMI between 18.5 and 24.9 is generally considered normal weight by the World Health Organization. However, optimal ranges may vary by age, gender, ethnicity, and individual body composition.
A BMI of 30.0 or higher is classified as obese. Obesity is further divided into Class I (30.0-34.9), Class II (35.0-39.9), and Class III or severe obesity (40.0 and above). Each class carries progressively higher health risks.
You do not need to convert the BMI number itself because BMI is a unitless ratio. However, you need to use the correct formula for your measurement system. The metric formula divides kg by m², while the imperial formula divides lbs by inches² and then multiplies by 703.
For children and teens aged 2 to 19, BMI is calculated the same way but interpreted using age- and sex-specific percentile charts from the CDC. A BMI at or above the 85th percentile is considered overweight, and at or above the 95th percentile is considered obese.
The factor 703 converts the imperial measurement units (pounds and inches) to produce the same BMI result as the metric formula. It accounts for the difference between kg/m² and lbs/in². Specifically, 703 ≈ 1 kg / 2.20462 lbs × (39.3701 in / 1 m)².
A high BMI is associated with increased risk of type 2 diabetes, cardiovascular disease, high blood pressure, certain cancers, sleep apnea, and joint problems. However, BMI alone does not diagnose health conditions and should be used alongside other assessments.
Yes. A BMI below 18.5 is classified as underweight and can indicate malnutrition, eating disorders, or other health issues. Being underweight is associated with weakened immune function, bone loss, anemia, and fertility problems.
Waist circumference, waist-to-hip ratio, body fat percentage (via DEXA scan or calipers), and waist-to-height ratio all provide additional information about body composition and health risk that BMI alone cannot capture.
Medical Disclaimer: BMI is a screening tool and not a diagnostic measure. It does not account for muscle mass, bone density, age, sex, or ethnic differences in body composition. This calculator is for informational purposes only and should not replace professional medical advice. Consult a healthcare provider for a comprehensive health assessment.