BMI & Body Fat Calculator
Calculate your BMI and estimated body fat percentage using your weight, height, age, and gender. Use it to screen for underweight, overweight, or obesity and understand your health risk category.
About this calculator
Body Mass Index (BMI) is calculated as BMI = weight / (height / 100)², where weight is in kilograms and height is in centimeters converted to meters. The result is a unitless number that classifies individuals into categories: underweight (<18.5), normal weight (18.5–24.9), overweight (25–29.9), and obese (≥30). Body fat percentage is then estimated using BMI alongside age and gender, because two people with identical BMIs can carry fat differently depending on these factors. Adding waist circumference further refines risk assessment, since abdominal fat is independently linked to cardiovascular and metabolic disease. Together these metrics give a more complete picture of health risk than BMI alone. Note that BMI is a screening tool, not a diagnostic measure.
How to use
Suppose a 35-year-old male weighs 85 kg and stands 175 cm tall. Step 1: Convert height — 175 / 100 = 1.75 m. Step 2: Square the height — 1.75² = 3.0625. Step 3: Divide weight by that value — 85 / 3.0625 ≈ 27.8. A BMI of 27.8 falls in the overweight range (25–29.9). Step 4: Enter age (35) and gender (male) to get an estimated body fat percentage. Step 5: Optionally add waist circumference (e.g., 92 cm) for an enhanced cardiovascular risk assessment.
Frequently asked questions
What is a healthy BMI range for adults?
For most adults, a BMI between 18.5 and 24.9 is considered healthy. Values below 18.5 indicate underweight, 25–29.9 indicates overweight, and 30 or above indicates obesity. These thresholds were established by the World Health Organization and are widely used in clinical settings. However, BMI does not distinguish between muscle and fat mass, so athletes or very muscular individuals may be misclassified. Always interpret BMI alongside other health indicators.
How is body fat percentage estimated from BMI, age, and gender?
Body fat percentage cannot be measured directly from BMI alone, but validated regression formulas use BMI, age, and gender as proxies. Generally, women carry a higher percentage of fat than men at the same BMI, and body fat tends to increase with age even when BMI stays constant. These formulas are derived from population studies comparing BMI with more precise measurements like DEXA scans. The estimate is useful for general screening but may differ from clinical body composition testing. For precision, methods like hydrostatic weighing or bioelectrical impedance are recommended.
Why does waist circumference matter alongside BMI for health risk?
Waist circumference captures abdominal (visceral) fat, which is metabolically more dangerous than subcutaneous fat stored elsewhere. Visceral fat is strongly associated with type 2 diabetes, cardiovascular disease, and metabolic syndrome, even in people with a normal BMI. Health guidelines suggest risk increases when waist circumference exceeds 94 cm in men or 80 cm in women. Combining waist measurement with BMI therefore gives a more accurate picture of cardiometabolic risk. This is why the calculator offers waist circumference as an optional but valuable input.