BMI Calculator
Calculate your Body Mass Index using either metric (kg and cm) or imperial (lbs and feet/ inches) measurements. BMI provides a rough indication of body weight status relative to height — but it has important limitations.
BMI limitations: BMI is a screening tool, not a diagnostic measure. It does not directly measure body fat and may misclassify athletes (high BMI from muscle mass) and older adults (normal BMI with excess body fat). Consult a healthcare professional for a complete health assessment.
What Is BMI?
BMI (Body Mass Index) is calculated by dividing weight in kilograms by height in meters squared. It was developed by Belgian statistician Adolphe Quetelet in the 19th century as a population-level measurement tool — not as an individual health diagnostic.
BMI Formula
Metric: BMI = weight (kg) ÷ height (m)² Imperial: BMI = (weight (lbs) ÷ height (in)²) × 703 Example: 70 kg, 175 cm (1.75 m): BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9
FAQ
What is a healthy BMI for adults?
The World Health Organization classifies BMI 18.5–24.9 as 'normal weight' for adults. However, these thresholds were developed on primarily European populations and may not be optimal for all ethnic groups. Some health organizations use lower BMI thresholds for Asian populations, where health risks appear at lower BMI values.
Is BMI accurate for athletes?
Not reliably. BMI cannot distinguish between muscle mass and fat mass. A muscular athlete may have a BMI in the 'overweight' range despite having low body fat. Conversely, a sedentary person with low muscle mass may have a 'normal' BMI while having unhealthy levels of body fat. For athletes, body composition measurements (DEXA scan, hydrostatic weighing, or skinfold calipers) are more informative.
Does BMI apply to children?
For children and teens (2–19 years), BMI is interpreted using age- and sex-specific percentile charts, not the fixed adult thresholds. A BMI at the 85th percentile for age and sex is considered 'overweight'; at the 95th percentile or above is 'obese.' The standard adult BMI thresholds do not apply to children.