BMI Calculator - Metric & Imperial, Healthy Weight Range

BMI (Body Mass Index) is a number calculated from height and weight that is used to screen for weight categories associated with health risks. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and has been used in clinical settings since the 1970s. The formula is straightforward: BMI = weight (kg) / height² (m²) for metric units, or BMI = (weight (lbs) / height² (inches)) × 703 for imperial units.

This calculator supports both metric (kg and cm) and imperial (lbs, feet, and inches) inputs. After calculating, it shows your BMI score, your WHO category, a visual gauge showing where you fall on the scale, and the healthy weight range for your specific height.

BMI is a population-level screening tool, not a diagnostic instrument. It does not measure body fat directly and has well-documented limitations for individuals - particularly athletes, older adults, and people of certain ethnicities. Use it as a starting point, not a final verdict on your health.

BMI does not distinguish between muscle mass and fat mass. A 200 lb bodybuilder and a 200 lb sedentary person have the same BMI, but very different body compositions and health profiles. This is why athletes and bodybuilders often fall into the "overweight" category despite having very low body fat percentages.

BMI also does not account for where fat is stored. Visceral fat (around the abdomen) carries significantly higher health risks than subcutaneous fat (under the skin). Two people with identical BMI scores can have very different risk profiles depending on their fat distribution. Waist circumference is a better predictor of metabolic risk than BMI alone.

Age and sex affect the relationship between BMI and body fat. Women generally have more body fat than men at the same BMI. Older adults tend to have more body fat at the same BMI as younger adults. Some health organizations recommend lower BMI thresholds for people of Asian descent, who face higher metabolic risks at lower BMI values than European populations.

For a more complete picture of your health, use BMI alongside waist circumference, body fat percentage (measured by DEXA scan or bioelectrical impedance), blood pressure, fasting glucose, and cholesterol levels. The WHO obesity fact sheet covers the health risks associated with excess body weight in more detail.

Switch between metric and imperial using the tabs above the input fields. For metric, enter your weight in kilograms and height in centimeters. For imperial, enter your weight in pounds and your height in feet and inches separately - the calculator handles the conversion internally.

Metric example: 70 kg, 175 cm. BMI = 70 / (1.75 × 1.75) = 70 / 3.0625 = 22.9. This falls in the Normal weight range.

Imperial example: 154 lbs, 5 feet 9 inches (69 inches total). BMI = (154 / (69 × 69)) × 703 = (154 / 4761) × 703 = 22.7. Same person, same result.

The healthy weight range shown after calculation is the weight range that corresponds to a BMI of 18.5 to 24.9 for your specific height. For a person who is 175 cm tall, this range is approximately 56.6 kg to 76.2 kg (124.7 lbs to 167.9 lbs).