Calculate your Body Mass Index instantly. WHO-standard categories, visual gauge and health advice — all free, no signup.
A BMI (Body Mass Index) Calculator is a free online tool that estimates body fatness based on your weight and height. BMI is a widely used screening tool by doctors, nutritionists and health authorities worldwide to classify individuals into weight categories — underweight, normal weight, overweight and obese — and assess potential health risks associated with excess or insufficient body weight.
BMI was developed by Belgian mathematician Adolphe Quetelet in the 19th century and later adopted by WHO as a standard population-level screening measure. While BMI does not directly measure body fat, it shows a moderate correlation with more accurate fat measurement methods such as DEXA scans and underwater weighing. For most adults, BMI provides a reliable indication of healthy weight ranges. In India, adjusted BMI thresholds (≥23 for overweight, ≥27.5 for obese) are sometimes used due to higher cardiometabolic risk at lower BMI values among South Asians.
| BMI Range | Category | Health Risk | Asian Cutoff |
|---|---|---|---|
| <18.5 | Underweight | Malnutrition risk | <18.5 |
| 18.5–24.9 | Normal Weight | Lowest risk | 18.5–22.9 |
| 25–29.9 | Overweight | Moderate risk | 23–27.4 |
| ≥30 | Obese | High risk | ≥27.5 |
The Ponderal Index (PI = weight/height³) is considered more accurate than BMI for very tall or very short individuals because it scales cubically with height. PI values between 11–14 kg/m³ indicate normal weight. BMI, while simpler, can misclassify muscular athletes as overweight and very sedentary individuals as normal. For general population screening, BMI remains the recommended first-line tool.
Step 1: Select your unit system (metric or imperial). Step 2: Enter your current body weight. Step 3: Enter your height. Step 4: Enter your age and gender. Step 5: Click Calculate to see your BMI, category, healthy weight range and how much weight to lose or gain to reach the normal range.
BMI does not account for muscle mass, bone density, fat distribution, age or ethnicity. Athletes with high muscle mass may be classified as overweight despite low body fat. Older adults may have normal BMI but excess visceral fat. Pregnant women should not use BMI as a health indicator. Always consult a doctor for a complete health assessment.
To achieve and maintain a healthy BMI, focus on a calorie-appropriate balanced diet with adequate protein, regular aerobic exercise (150 min/week moderate intensity), strength training 2–3 times per week, adequate sleep (7–9 hours) and stress management. Small, consistent lifestyle changes over time are more effective than crash diets.
Two main methods: Quetelet Index (standard BMI = weight/height²) and Ponderal Index (weight/height³, better for extreme heights). WHO uses standard BMI globally. IOTF (International Obesity Task Force) provides age-sex specific BMI cutoffs for children using growth curves. This calculator uses the standard WHO adult BMI formula with WHO risk categories.