Calculate your Body Mass Index from your height and weight, in metric or imperial units, and see which category you fall into.
Body Mass Index (BMI) is a simple screening number that relates your weight to your height. It is widely used as a quick indicator of whether you are in a healthy weight range.
BMI = weight (kg) ÷ height (m)²
BMI is a quick screening tool, but it has real blind spots. Because it only uses height and weight, it can't tell muscle from fat. A muscular athlete may register as "overweight" or even "obese" despite having very low body fat, while an older person who has lost muscle may fall in the "healthy" range while carrying excess fat. BMI also doesn't account for where fat is stored — abdominal fat carries more health risk than fat on the hips and thighs. For these reasons, doctors use BMI alongside other measures rather than on its own.
If you want a fuller picture of your health, combine BMI with a few other simple metrics. Waist circumference indicates abdominal fat — a waist over 40 inches (102 cm) for men or 35 inches (88 cm) for women signals higher risk. Waist-to-height ratio (keeping your waist under half your height) is a strong, easy indicator. Body fat percentage, measured with calipers, smart scales, or a DEXA scan, distinguishes fat from lean mass directly. No single number tells the whole story, so think of BMI as one data point among several.
The adult BMI categories above don't apply to everyone. For children and teens, BMI is interpreted using age- and sex-specific percentile charts because healthy ranges change as kids grow. For athletes with high muscle mass, BMI overestimates body fat and should be treated with caution. For older adults, a slightly higher BMI is sometimes associated with better outcomes, and muscle loss can mask excess fat. If you fall into one of these groups, a healthcare professional can interpret your numbers in context.
If your BMI falls outside the healthy range, the goal isn't to obsess over the number but to use it as motivation for sustainable habits: balanced nutrition, regular physical activity, adequate sleep, and stress management. Small, consistent changes move BMI in the right direction over time. Always consult a doctor or registered dietitian before starting a significant weight-loss or weight-gain program, especially if you have underlying health conditions.
BMI equals your weight in kilograms divided by your height in metres squared (kg/m²). In imperial units, the formula is 703 × weight in pounds ÷ height in inches squared. The calculator above handles both unit systems for you.
For most adults, a BMI between 18.5 and 24.9 is considered healthy. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is classified as obese. These ranges are general guidelines and may not apply to athletes, children, or older adults.
No. BMI doesn't measure body fat directly, so it can misclassify very muscular people and may underestimate fat in those who have lost muscle. It's a useful population-level screening tool but not a personal diagnosis.
For an individual, waist circumference, waist-to-height ratio, and body fat percentage give more insight into health risk than BMI alone. Doctors often look at several measures together rather than relying on a single number.
The adult BMI formula and categories are the same for men and women. However, at the same BMI women tend to carry more body fat than men, which is one reason BMI is best interpreted alongside other measurements.