Body Mass Index (BMI) is a simple number calculated from your weight and height. It gives you a quick snapshot of whether your weight falls within a healthy range for your height. Doctors, schools, and health organisations worldwide use BMI as a first step in assessing weight-related health risks.
Choose Metric (kg/cm) or Imperial (lbs/inches), enter your weight and height, then click Calculate. Your BMI score and category appear instantly. You can also enter your age — while it does not affect the BMI result, it is useful for your own reference.
BMI is a screening tool, not a diagnosis. It does not measure body fat directly. Athletes and people with high muscle mass often show a high BMI despite being healthy. Older adults may have a normal BMI but still carry excess body fat. Always consult a healthcare professional for a complete health picture.
Metric: BMI = Weight (kg) ÷ Height (m)². Imperial: BMI = (Weight in lbs × 703) ÷ Height (inches)².
The Body Mass Index formula divides your weight by the square of your height. In metric units, you take your weight in kilograms and divide it by your height in metres squared. For example, a person who weighs 75 kg and stands 1.75 m tall has a BMI of 75 divided by 3.0625, which equals 24.5. In imperial units, the formula multiplies your weight in pounds by 703, then divides by your height in inches squared. A person weighing 165 lbs at 5 feet 9 inches (69 inches) would calculate 165 times 703 divided by 4,761, giving a BMI of approximately 24.4. Both formulas produce the same result regardless of which measurement system you prefer.
The World Health Organization defines four primary BMI categories for adults. A BMI below 18.5 is classified as underweight, which may signal nutritional deficiency or an underlying health condition worth discussing with a doctor. A BMI between 18.5 and 24.9 falls within the normal weight range and is generally associated with the lowest health risks. A BMI of 25.0 to 29.9 is considered overweight, indicating a moderately elevated risk for conditions such as type 2 diabetes and cardiovascular disease. A BMI of 30.0 or above is classified as obese, with further subdivisions at 35 and 40 reflecting increasingly serious health risks. These thresholds serve as population-level guidelines and should always be interpreted alongside other clinical indicators.
While the BMI calculator is a useful screening tool, it has well-documented limitations. BMI does not distinguish between muscle mass, bone density, and body fat. Athletes and people who strength-train regularly may register as overweight or obese despite having low body fat percentages. Conversely, older adults who have lost muscle mass may appear to have a normal BMI while carrying excess fat. Research also shows that BMI thresholds may not apply equally across ethnic groups. For instance, people of South Asian descent tend to carry higher cardiovascular risk at lower BMI values, while some Pacific Islander populations may be healthier at slightly higher readings. Age and sex also influence how BMI relates to actual body fat. For a complete health assessment, consider supplementing your BMI result with waist circumference measurements, body fat analysis, and professional medical advice.