Advanced BMI Calculator

BMI (Body Mass Index) is a measure of body fat based on height and weight. Formula: BMI = weight (kg) ÷ height² (m²). Example: 70 kg person at 1.70 m height: BMI = 70 ÷ (1.7 × 1.7) = 24.2. It's a quick screening tool for weight categories but doesn't measure body fat directly.

WHO BMI categories: Underweight (<18.5), Normal (18.5-24.9), Overweight (25-29.9), Obese Class I (30-34.9), Obese Class II (35-39.9), Obese Class III (≥40). For Asians, different cutoffs apply: Normal (<23), Overweight (23-27.5), Obese (>27.5) due to higher disease risk at lower BMIs.

Research shows that Asians (including Indians, Chinese, Japanese) develop obesity-related diseases like Type 2 Diabetes at lower BMIs than Caucasians. WHO Asia-Pacific guidelines recommend: Normal BMI < 23 (vs 25 for WHO), Overweight ≥ 23, Obese ≥ 27.5. This is why our calculator offers both standards.

For Indians and South Asians, a healthy BMI is 18.5-22.9. A BMI of 23-24.9 indicates overweight, and ≥25 indicates obesity. These are lower than WHO cutoffs because Indians have higher body fat percentage at the same BMI and develop metabolic diseases earlier. Use Asian standard in this calculator.

BMI Prime is the ratio of your BMI to the upper limit of healthy BMI. Formula: BMI Prime = Your BMI ÷ 25 (or 23 for Asian). A BMI Prime of 1.0 means you're at the upper limit of normal weight. Below 1.0 = healthier weight range. Above 1.0 = overweight/obese. It's useful for comparing different populations.

Ideal weight range is calculated using healthy BMI range (18.5-25 for WHO, 18.5-23 for Asian). Formula: Weight = BMI × Height² (m²). For 170 cm (WHO): Min = 18.5 × 1.7² = 53.5 kg, Max = 25 × 1.7² = 72.3 kg. Our calculator shows this range automatically.

BMR is the number of calories your body burns at complete rest to maintain vital functions (breathing, circulation, cell production). We use Mifflin-St Jeor formula: Men: BMR = 10×weight + 6.25×height - 5×age + 5. Women: BMR = 10×weight + 6.25×height - 5×age - 161. It's the baseline for calculating daily caloric needs.

No. BMI doesn't distinguish between muscle and fat mass. Athletes and bodybuilders with high muscle mass may show 'overweight' BMI despite having low body fat. For them, body fat percentage, waist-to-hip ratio, or DEXA scans are better measures. BMI works best for average adults.

Daily caloric needs = BMR × Activity Factor. Sedentary (office job): BMR × 1.2. Moderate (light exercise 3-5 days): BMR × 1.55. Active (hard exercise 6-7 days): BMR × 1.725. To lose weight, create a 500 calorie deficit. To gain, add 500 calories. Our calculator shows all three activity levels.

High BMI increases risk of: Type 2 Diabetes (most common), Heart Disease and Stroke, High Blood Pressure, Osteoarthritis, Sleep Apnea, Certain Cancers (breast, colon), Fatty Liver Disease, Kidney Disease. Risk increases significantly above BMI 30. Even modest weight loss (5-10%) reduces risk substantially.

Frame Size (Small, Medium, Large) is determined by wrist circumference relative to height. Formula: Height (cm) ÷ Wrist (cm). For men: >10.4 = Small, 9.6-10.4 = Medium, <9.6 = Large. For women: >11.0 = Small, 10.1-11.0 = Medium, <10.1 = Large. Frame size affects ideal weight—larger frames can carry more weight healthily.

Waist-to-Hip Ratio (WHR) measures fat distribution. Formula: Waist circumference ÷ Hip circumference. Healthy WHR: Men <0.9, Women <0.8. High WHR indicates visceral fat (belly fat), which is more dangerous than subcutaneous fat. High WHR increases cardiovascular disease risk even with normal BMI.

Four scientific formulas for ideal weight: 1) Devine (1974): Most widely used in medicine. 2) Robinson (1983): More conservative estimates. 3) Miller (1983): Higher weights than Devine. 4) Hamwi (1964): Traditional formula. All use height but give slightly different results. Our calculator shows all four for comparison.

Heart rate zones optimize workout effectiveness. We use Karvonen method (accounts for resting heart rate). Fat Burn Zone: 50-60% HRR—burns more fat as percentage of calories. Cardio Zone: 60-70% HRR—improves cardiovascular fitness. Peak Zone: 70-85% HRR—maximum performance training. Max HR = 220 - age.

Daily water intake depends on weight and activity. Base formula: 35 ml per kg of body weight. Add 500 ml for each activity level above sedentary. Example: 70 kg moderately active person needs ~2,800 ml (2.8 L). Athletes, hot climates, and pregnant women need more. Our calculator adjusts for your activity level.