BMI (Body Mass Index) is a measure of body fat based on height and weight that applies to adult men and women. It's calculated by dividing weight in kilograms by height in meters squared (kg/m²). BMI is used worldwide as a simple screening tool to identify potential weight-related health problems. Developed by Belgian statistician Adolphe Quetelet in the 1830s, BMI provides a quick assessment but doesn't directly measure body fat percentage, muscle mass, or fat distribution. It's one indicator among many for overall health.

What is a healthy BMI range?

A healthy BMI for adults ranges from 18.5 to 24.9 according to WHO standards. Below 18.5 is considered underweight (increased risk of malnutrition, weakened immunity, osteoporosis). 25.0 to 29.9 is overweight (moderate risk of cardiovascular disease, diabetes, hypertension). 30.0 or higher is obese (high risk of serious health conditions including heart disease, stroke, type 2 diabetes, certain cancers). However, BMI doesn't account for muscle mass, bone density, body composition, or fat distribution. Athletes with high muscle mass may have high BMI but low body fat. Always consult healthcare providers for personalized assessment.

Is BMI accurate for everyone?

No, BMI has significant limitations and isn't accurate for several groups: (1) Athletes and bodybuilders - high muscle mass inflates BMI despite low body fat, (2) Older adults - muscle loss with age makes BMI less relevant, (3) Pregnant or breastfeeding women - weight fluctuation is normal and healthy, (4) Growing children and teenagers - use age/sex-specific BMI percentiles instead, (5) People with different ethnicities - Asian populations have higher health risks at lower BMI (23-27.5 considered overweight). BMI also ignores fat distribution - visceral (belly) fat is more dangerous than subcutaneous fat. Better alternatives: body fat percentage, waist circumference, waist-to-hip ratio. BMI is a starting point, not definitive health measure.

What are the BMI categories and health risks?

BMI categories and associated health risks: (1) Underweight (<18.5) - risks include malnutrition, weakened immune system, anemia, osteoporosis, fertility issues, increased mortality, (2) Normal (18.5-24.9) - optimal health range, lowest risk of weight-related diseases, (3) Overweight (25-29.9) - moderate increased risk of hypertension, heart disease, type 2 diabetes, sleep apnea, gallstones, osteoarthritis, (4) Obese Class I (30-34.9) - high risk, (5) Obese Class II (35-39.9) - very high risk, (6) Obese Class III (40+) - extremely high risk, severe health complications. However, individual health varies based on genetics, lifestyle, muscle mass, fat distribution, diet, exercise, and other factors beyond BMI. Two people with identical BMI can have vastly different health profiles.

How can I improve my BMI?

To achieve a healthy BMI through sustainable lifestyle changes: (1) Nutrition - focus on whole foods (vegetables, fruits, lean proteins, whole grains, healthy fats), control portions, limit processed foods, sugary drinks, and excessive alcohol, create moderate calorie deficit (500 cal/day for 1 lb/week loss), (2) Exercise - aim for 150 minutes moderate or 75 minutes vigorous exercise weekly, include strength training 2-3 times/week to build muscle, add daily movement (walking, stairs), (3) Lifestyle - get 7-9 hours quality sleep, manage stress (meditation, yoga), stay hydrated (8+ glasses water daily), track progress but focus on how you feel not just numbers, (4) Support - consider nutritionist, personal trainer, support groups, medical supervision if BMI >30. Gradual changes (1-2 lbs/week) are safer and more sustainable than crash dieting. Focus on health improvements beyond BMI: energy, mood, fitness, blood markers.

What's the difference between BMI and body fat percentage?

BMI and body fat percentage measure different things: BMI is height-to-weight ratio (doesn't measure composition), while body fat percentage is the proportion of fat mass to total body weight (direct composition measure). Examples show the difference: (1) Muscular athlete - BMI 28 (overweight), body fat 12% (excellent), (2) Sedentary person - BMI 22 (normal), body fat 30% (overfat/skinny fat). Healthy body fat ranges: Men 10-20% (athletes 6-13%), Women 18-28% (athletes 14-20%). Body fat percentage is more accurate for health assessment but requires special equipment (DEXA scan, BodPod, bioelectrical impedance, skinfold calipers). BMI is convenient screening tool; body fat is precise diagnostic tool. Both have value in different contexts.

Does BMI differ by age, gender, or ethnicity?

Yes, BMI interpretation should consider demographics: AGE - Children/teens use age-sex-specific BMI percentiles (not adult cutoffs). Older adults (65+) may be healthier at slightly higher BMI (23-28) due to muscle loss and frailty risks. GENDER - Men typically have more muscle mass, women more essential body fat, but same BMI cutoffs apply (controversial). Some suggest different standards. ETHNICITY - Asian populations have higher health risks at lower BMI. WHO Asian cutoffs: Normal 18.5-22.9, Overweight 23-27.4, Obese ≥28. This applies to Chinese, Japanese, South Asian populations. Pacific Islanders and some Black populations may have higher healthy BMI ranges due to bone density and muscle mass. Pregnant women should NOT use standard BMI for health assessment. Always use population-specific guidelines when available.

What's more important: BMI or waist circumference?

Waist circumference is often MORE important than BMI for predicting health risks. Why? It directly measures abdominal (visceral) fat, which surrounds organs and is metabolically active, releasing inflammatory substances. Visceral fat strongly predicts cardiovascular disease, type 2 diabetes, and metabolic syndrome - even at normal BMI. High-risk waist circumference: Men >40 inches (102 cm), Women >35 inches (88 cm). Waist-to-hip ratio (WHR) is even better: Men >0.90, Women >0.85 = high risk. 'Apple shape' (belly fat) is riskier than 'pear shape' (hip/thigh fat). Someone with BMI 27 and waist 32 inches is healthier than someone with BMI 23 and waist 38 inches. Best approach: Monitor BOTH BMI and waist circumference for complete picture. Losing inches often matters more than losing pounds.

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BMI Calculator (Body Mass Index)

Calculate your Body Mass Index (BMI), understand your weight category, and get personalized health recommendations based on WHO standards.

BMI Calculator (Body Mass Index)

Weight (kg)*

Height (cm)*

What is BMI Calculator (Body Mass Index)?

A Body Mass Index (BMI) calculator measures your body fat based on height and weight that applies to adult men and women. BMI is a screening tool to identify whether you're underweight, normal weight, overweight, or obese. While not a diagnostic tool for body fatness or health, BMI is widely used by healthcare professionals as a quick assessment method. It provides a reliable indicator for most people to understand their weight category and potential health risks associated with being over or underweight.

Key Benefits & Use Cases

Track your weight loss or gain progress objectively with scientifically-backed measurements used by doctors worldwide. Set realistic fitness goals based on your BMI category, understand health risks associated with your current weight, and monitor changes over time. Whether you're working with a nutritionist, starting a fitness program, or managing medical conditions like diabetes or heart disease, BMI provides a standardized metric for tracking progress. Free, instant, and clinically accurate calculations help millions make informed health decisions daily.

How to Use This Calculator

Select your measurement system (metric or imperial), enter your height and current weight, then click calculate. Results show your BMI number, weight category (underweight, normal, overweight, obese), and health insights. For accuracy, measure your weight in the morning before eating, and ensure height measurements are precise. Track your BMI monthly to see trends rather than focusing on daily fluctuations. Remember that BMI doesn't account for muscle mass, so athletes may show higher numbers despite being healthy.