Free Body Mass Index (BMI) Calculator for Adults

Body Mass Index (BMI) is calculated as weight in kilograms divided by height in meters squared (kg/m²). It is a simple screening tool developed by Adolphe Quetelet in the 19th century and adopted by the WHO as a population-level weight classification system.

Underweight: below 18.5 | Healthy weight: 18.5–24.9 | Overweight: 25.0–29.9 | Obese class I: 30.0–34.9 | Obese class II: 35.0–39.9 | Obese class III: 40.0 and above. These cut-offs apply to adults and are the same regardless of age or sex.

BMI does not distinguish between fat mass and muscle mass. Athletes and bodybuilders can have a BMI in the "overweight" or "obese" range despite having low body fat and excellent health. Conversely, older adults can have a normal BMI but high fat percentage (a condition called "skinny fat" or sarcopenic obesity).

Standard BMI cut-offs apply only to adults (20+). For children and teens, BMI-for-age percentile charts must be used because body composition changes significantly during growth. A pediatric BMI calculator uses age and sex-specific percentiles.

A healthy BMI of 18.5–24.9 corresponds to specific weight ranges per height. For example: 170 cm (5 ft 7 in) → 53–72 kg (117–158 lbs). 180 cm (5 ft 11 in) → 60–81 kg (132–178 lbs). Our calculator shows your personal healthy range after you enter your height.