Calculate your Body Mass Index (BMI) using either metric or imperial measurements. Get your WHO health category instantly along with a personalized interpretation of your result and what steps to consider.
Body Mass Index (BMI) is a numerical measure derived from a person's height and weight. The formula is BMI = weight (kg) ÷ height (m)². For imperial measurements, the formula is BMI = (weight in lbs × 703) ÷ height in inches². The World Health Organization established the current BMI categories in the 1990s as a population-level screening tool to flag potential weight-related health risks.
BMI is widely used in clinical settings because it requires no special equipment — just a scale and a measuring tape. Despite its simplicity, it correlates reasonably well with more precise measures of body fat in large population studies, making it useful as a first-level screening indicator. However, it has significant limitations that are important to understand when interpreting your result.
Person: 175 cm tall, 80 kg. BMI = 80 ÷ (1.75)² = 80 ÷ 3.0625 = 26.1 — Overweight. To reach the top of the normal range (24.9), this person would need to weigh approximately 76.2 kg.
Person: 5'8" (68 inches) tall, 160 lbs. BMI = (160 × 703) ÷ 68² = 112,480 ÷ 4,624 = 24.3 — Normal Weight. This person is near the upper boundary of the healthy range.
A 6'0" (183 cm) male athlete weighing 220 lbs (100 kg): BMI = 100 ÷ (1.83)² = 29.9 — Overweight. However, if this person is a football player or bodybuilder with 10% body fat, they are clearly not overweight — they carry exceptional muscle mass that BMI cannot distinguish from fat.
BMI cannot differentiate between fat mass and lean mass (muscle, bone, water). This creates systematic misclassification in two directions. Highly muscular individuals often have elevated BMIs despite low body fat percentages. Conversely, older adults or sedentary individuals can have a "normal" BMI while carrying excessive body fat and very little muscle — a condition sometimes called "skinny fat" or normal-weight obesity.
BMI also does not account for fat distribution. Visceral fat (stored around internal organs in the abdominal area) is far more metabolically dangerous than subcutaneous fat (stored under the skin). Two people with identical BMIs can have very different health risk profiles depending on where their fat is stored. Waist circumference measurements are a better predictor of metabolic risk than BMI alone.
If your BMI is in the normal range, use it as one confirmation of a healthy weight — but continue monitoring other health indicators like blood pressure, cholesterol, and fitness level. If your BMI is in the overweight or obese range, it's a useful prompt to discuss health risks with your doctor, but it should not be interpreted as a diagnosis. A comprehensive health assessment including blood work, blood pressure, physical fitness evaluation, and body composition measurement provides a far more complete picture than BMI alone.
No. BMI is most accurate for sedentary or lightly active adults of average build. It frequently misclassifies highly muscular individuals (flagging them as overweight or obese) and older adults who have lost muscle mass (showing a normal BMI despite high body fat). Athletes, bodybuilders, and pregnant women should not rely on BMI as a health indicator.
The standard WHO BMI categories (18.5–24.9 for normal weight) apply to both men and women. However, women naturally carry more essential body fat than men, so the same BMI can represent different body compositions by gender. Some researchers argue that women should have slightly higher upper thresholds, but most clinical guidelines still use the same ranges.
BMI decreases when weight decreases or height increases. Since height is fixed in adulthood, BMI reduction requires weight loss through a calorie deficit. A deficit of 500 calories per day leads to approximately 1 pound of weight loss per week. Sustainable weight loss combines reduced caloric intake with regular physical activity. Consult a healthcare provider before starting any weight loss program.
A BMI below 17.5 is often used as a clinical indicator of significant underweight, and below 15 is associated with severe malnutrition. If your BMI is below 18.5 and you have experienced unexplained weight loss, fatigue, or other symptoms, speak with a healthcare provider promptly.
The standard BMI categories are the same for adults 20 and older. However, for children and teenagers, BMI is age and sex-specific and compared against growth charts rather than fixed thresholds. For older adults (65+), some research suggests that a slightly higher BMI (around 25–27) may actually be associated with better outcomes, though this is still debated.