BMI Calculator

What Is BMI and How Is It Calculated?

Body Mass Index (BMI) is a screening tool calculated from your weight and height: BMI = weight (kg) ÷ height (m)². In imperial units, the formula is BMI = (weight in lbs ÷ height in inches²) × 703. The result is a dimensionless number used to broadly categorise individuals into weight status groups as defined by the World Health Organisation (WHO).

WHO BMI Categories

• Below 18.5 — Underweight: associated with nutritional deficiency, immune weakness, and osteoporosis.
• 18.5 – 24.9 — Normal weight: lowest statistical risk for most metabolic conditions.
• 25.0 – 29.9 — Overweight: increased risk of type 2 diabetes, hypertension, and cardiovascular disease.
• 30.0 and above — Obese: high risk; further divided into Class I (30–34.9), Class II (35–39.9), and Class III (40+).

BMI Prime

BMI Prime is the ratio of your BMI to the upper limit of the normal range (25). A BMI Prime below 1.0 means you are in or below the normal range; above 1.0 means overweight or obese. It simplifies comparisons by expressing BMI as a single proportion rather than requiring knowledge of the category boundaries.

Adjusted Thresholds for South Asians

Research consistently shows South Asians carry higher body fat and face elevated cardiometabolic risk at lower BMI values than the WHO global thresholds suggest. Many Indian clinical guidelines use 23 kg/m² as the overweight threshold and 27.5 kg/m² as the obese threshold. This calculator uses standard WHO thresholds — consult your doctor for guidance specific to your ethnic background.

Medical disclaimer: BMI is a screening tool only, not a clinical diagnosis. Consult a qualified healthcare professional for personalised health assessment.