BMI Calculator
Calculate your Body Mass Index (BMI) from your height and weight.
BMI is a general screening measure and does not diagnose body fatness or health. Consult a healthcare professional for medical advice.
About this tool
Body Mass Index (BMI) is a simple screening measure that estimates whether a person's weight is in a healthy range for their height, using only two numbers: weight and height. It's widely used by health organizations worldwide precisely because it's quick to calculate and doesn't require special equipment.
The formula was devised in the 1830s by Belgian mathematician Adolphe Quetelet for population studies, not individual diagnosis. It was later popularized as a screening tool because it correlates reasonably well with body fat at a population level, even though it has well-documented limitations for individuals.
This tool is for general information only, and is not medical advice. BMI does not directly measure body fat and can be misleading for athletes with high muscle mass, pregnant people, older adults who have lost muscle, and children (who need age- and sex-specific charts instead). Always consult a healthcare professional for a full picture of your health.
Formula
Metric: BMI = kg / m². Imperial: BMI = (lbs / in²) x 703
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Frequently asked questions
- How is BMI calculated?
- BMI is calculated as weight in kilograms divided by height in meters squared (kg/m²), or weight in pounds divided by height in inches squared, multiplied by 703.
- Is BMI accurate for everyone?
- BMI is a general screening tool and does not account for muscle mass, bone density, or body composition. It tends to overestimate body fat in muscular people and underestimate it in older adults who have lost muscle mass, and it should not replace advice from a healthcare professional.
- Who created BMI and why?
- BMI is based on a formula devised in the 1830s by Belgian mathematician Adolphe Quetelet, originally to study population-level statistics rather than individual health. It was later adopted by health organizations as a simple, low-cost screening tool because it only requires height and weight.
- What are the standard BMI categories?
- The World Health Organization defines the adult categories used in this calculator as: underweight (below 18.5), normal weight (18.5–24.9), overweight (25–29.9), and obese (30 and above).
- What should I use instead of, or alongside, BMI?
- Waist circumference, waist-to-hip ratio, and body fat percentage (measured by skinfold calipers, bioelectrical impedance, or DEXA scans) can give a more complete picture, since they account for where and how body fat is distributed. A healthcare provider can advise which measures matter most for you.