BMI Calculator

Calculate your Body Mass Index and find your healthy weight range

📏 Height

⚖️ Weight

BMI Categories

Category	BMI Range
Severe Thinness	< 16
Moderate Thinness	16 - 17
Mild Thinness	17 - 18.5
Normal	18.5 - 25
Overweight	25 - 30
Obese Class I	30 - 35
Obese Class II	35 - 40
Obese Class III	> 40

⚠️ BMI is a screening tool and does not diagnose health. It does not account for muscle mass, bone density, or body composition. Consult a healthcare professional for personalized advice.

Calculate your Body Mass Index (BMI) instantly using metric (kg/cm) or imperial (lbs/ft) units. Get your BMI score, weight category classification (underweight, normal, overweight, obese), and personalized healthy weight range based on WHO standards. View your position on the BMI scale with visual indicators and discover your ideal weight target (BMI 22). Understand BMI categories from severe thinness (< 16) to obese class III (≥ 40) with health implications for each range. All calculations follow the standard BMI formula: weight (kg) / height (m)². Perfect for health monitoring, fitness goal setting, medical consultations, and insurance applications. Note: BMI is a screening tool and doesn't account for muscle mass, bone density, age, or ethnicity—consult healthcare professionals for personalized health assessments.

BMI (Body Mass Index) is a numerical value derived from your weight and height, used as a screening tool to categorize individuals into weight status groups. The formula was invented by Belgian mathematician Adolphe Quetelet in 1832 (originally called the Quetelet Index) during his work on 'social physics'—applying statistics to human characteristics. The term 'Body Mass Index' was coined by physiologist Ancel Keys in 1972. BMI is calculated as: weight (kg) / [height (m)]². For imperial units: [weight (lbs) / height (inches)²] × 703. The World Health Organization (WHO) established standard BMI categories in 1995: Underweight (< 18.5), Normal (18.5-24.9), Overweight (25-29.9), Obese Class I (30-34.9), Class II (35-39.9), Class III (≥ 40). BMI correlates with body fat percentage and health risks: higher BMI increases risk of type 2 diabetes (2-4× at BMI 30+), cardiovascular disease (2× at BMI 30+), hypertension, certain cancers, and sleep apnea. However, BMI has limitations: it doesn't distinguish muscle from fat (bodybuilders may be classified as 'overweight'), doesn't account for fat distribution (visceral vs subcutaneous), and varies by ethnicity—Asian populations have higher health risks at lower BMIs, leading WHO to recommend modified cutoffs for Asian populations (overweight at 23, obese at 27.5).

Health Screening & Medical Checkups

Doctors use BMI as a quick screening tool during annual physicals to identify potential weight-related health risks. BMI ≥ 30 triggers additional assessments for diabetes, hypertension, and cholesterol. Insurance companies use BMI for risk assessment and premium calculations—some charge 10-50% more for BMI ≥ 30.

Weight Loss & Fitness Goal Setting

Establish baseline BMI before starting diet or exercise programs. Track progress toward healthy BMI range (18.5-24.9). Losing 5-10% of body weight (typically 1-2 BMI points) significantly reduces health risks even if you remain in overweight category. Set realistic goals: 0.5-1 kg (1-2 lbs) per week is sustainable.

Pregnancy Planning & Prenatal Care

Pre-pregnancy BMI determines recommended weight gain: underweight (BMI < 18.5) should gain 28-40 lbs, normal (18.5-24.9) 25-35 lbs, overweight (25-29.9) 15-25 lbs, obese (≥ 30) 11-20 lbs. BMI ≥ 30 increases risks of gestational diabetes, preeclampsia, and cesarean delivery. Doctors monitor BMI throughout pregnancy.

Sports & Athletic Performance

Athletes in weight-class sports (boxing, wrestling, MMA) use BMI to track weight categories. However, BMI is unreliable for athletes—muscle weighs more than fat, so muscular athletes often have 'overweight' BMI (25-29.9) despite low body fat. Use body fat percentage or waist-to-hip ratio instead for athletes.

Medication Dosing & Anesthesia

Some medications require dosage adjustments based on BMI. Anesthesiologists use BMI to calculate anesthesia doses and assess intubation difficulty. BMI ≥ 35 increases surgical risks and may require specialized equipment. Bariatric surgery eligibility typically requires BMI ≥ 40 or BMI ≥ 35 with comorbidities.

Military & Occupational Requirements

Military branches have BMI standards: U.S. Army requires BMI < 25 (or pass body fat test if higher). Airlines, police, and firefighters may have BMI requirements for physical fitness standards. Some countries use BMI for visa medical examinations—New Zealand requires BMI < 35 for certain visa categories.

BMI calculation uses a simple mathematical formula: BMI = weight (kg) / [height (m)]². For example, a person weighing 70 kg and 1.75 m tall: BMI = 70 / (1.75 × 1.75) = 70 / 3.0625 = 22.9 (Normal weight). For imperial units, the formula includes a conversion factor: BMI = [weight (lbs) / height (inches)²] × 703. Example: 154 lbs, 5'9" (69 inches): BMI = (154 / 69²) × 703 = (154 / 4,761) × 703 = 22.7. The 703 conversion factor comes from converting pounds to kilograms (÷ 2.205) and inches to meters (÷ 39.37), then squaring: (39.37² / 2.205) ≈ 703. After calculating BMI, the value is compared to WHO categories: < 16 (Severe Thinness), 16-16.9 (Moderate Thinness), 17-18.4 (Mild Thinness), 18.5-24.9 (Normal), 25-29.9 (Overweight), 30-34.9 (Obese Class I), 35-39.9 (Obese Class II), ≥ 40 (Obese Class III). Healthy weight range is calculated by solving the BMI formula for weight at BMI 18.5 and 24.9: Min weight = 18.5 × height² (m), Max weight = 24.9 × height² (m). Ideal weight uses BMI 22 (middle of healthy range): Ideal = 22 × height² (m). For a 1.75 m person: Min = 18.5 × 3.0625 = 56.7 kg, Max = 24.9 × 3.0625 = 76.3 kg, Ideal = 22 × 3.0625 = 67.4 kg. BMI doesn't measure body fat directly—it's a proxy based on population studies showing correlation between BMI and body fat percentage (r = 0.7-0.8). For accurate body composition, use DEXA scans, bioelectrical impedance, or skinfold calipers.

BMI Range	< 18.5	18.5 - 24.9	25 - 29.9	≥ 30
Health Risk	Malnutrition, osteoporosis, anemia	Lowest risk (baseline)	Moderate risk (1.5× baseline)	High risk (2-4× baseline)
Type 2 Diabetes Risk	Low	Baseline (1×)	2× increased	4-7× increased
Cardiovascular Disease	Increased (malnutrition)	Baseline (1×)	1.5× increased	2-3× increased
Life Expectancy Impact	-4 to -6 years	Baseline (longest)	-1 to -3 years	-5 to -10 years (Class III)
Recommended Action	Gain weight, consult doctor	Maintain current weight	Lose 5-10% body weight	Medical supervision, lose 10%+
Asian Population Cutoffs	< 18.5 (same)	18.5 - 22.9 (lower)	23 - 27.4 (lower)	≥ 27.5 (lower)

Our BMI calculator uses the standard WHO formula with precision to two decimal places. The calculation is mathematically accurate for the formula itself, but BMI has inherent limitations as a health metric. BMI doesn't account for: (1) Muscle mass—bodybuilders and athletes often have 'overweight' or 'obese' BMI despite low body fat. Arnold Schwarzenegger at peak had BMI 30+ (obese) with 5% body fat. (2) Age—older adults naturally lose muscle and gain fat, so same BMI at 70 vs 30 represents different body composition. (3) Sex—women naturally have 6-11% higher body fat than men at same BMI. (4) Ethnicity—Asian populations have higher health risks at lower BMIs; Pacific Islanders have lower risks at higher BMIs. (5) Fat distribution—visceral fat (around organs) is more dangerous than subcutaneous fat, but BMI doesn't distinguish. (6) Bone density—people with dense bones weigh more without increased health risk. For more accurate health assessment, combine BMI with: waist circumference (men > 102 cm / 40 in, women > 88 cm / 35 in indicates high risk), waist-to-hip ratio (> 0.90 men, > 0.85 women = high risk), body fat percentage (men 18-24%, women 25-31% = healthy), and blood tests (glucose, cholesterol, blood pressure). BMI is best used as a population-level screening tool, not individual diagnostic tool.

Frequently Asked Questions

What is a healthy BMI for my age and gender?

WHO's standard healthy BMI range (18.5-24.9) applies to adults 18-65 regardless of gender. However, women naturally have 6-11% higher body fat than men at the same BMI. For older adults (65+), slightly higher BMI (23-27) may be healthier—studies show lowest mortality at BMI 25-27 for seniors. Children and teens use age and sex-specific BMI percentiles, not adult categories. For Asians, healthy range is 18.5-22.9 due to higher health risks at lower BMIs.

Is BMI accurate for athletes and muscular people?

No, BMI is inaccurate for athletes and very muscular individuals. Muscle weighs more than fat, so bodybuilders, rugby players, and strength athletes often have 'overweight' (BMI 25-29.9) or 'obese' (BMI 30+) classifications despite low body fat (8-15%). For example, NFL running backs average BMI 30.5 with 10% body fat. Athletes should use body fat percentage (men < 18%, women < 25% = athletic) or waist-to-hip ratio instead of BMI.

How much should I weigh for my height?

For a healthy BMI (18.5-24.9), calculate: Min weight = 18.5 × height² (meters), Max weight = 24.9 × height² (meters). Examples: 5'5" (1.65 m): 50.3-67.6 kg (111-149 lbs). 5'9" (1.75 m): 56.7-76.3 kg (125-168 lbs). 6'0" (1.83 m): 62.0-83.4 kg (137-184 lbs). Ideal weight (BMI 22): 22 × height² (meters). These are guidelines—individual ideal weight varies based on muscle mass, frame size, and body composition.

What BMI is considered obese?

BMI ≥ 30 is classified as obese by WHO standards. Obesity is further divided: Class I (30-34.9), Class II (35-39.9), Class III (≥ 40, also called severe or morbid obesity). Obesity significantly increases health risks: type 2 diabetes (4-7× higher), heart disease (2-3×), stroke (2×), certain cancers (1.5-2×), sleep apnea (4×), and osteoarthritis (4-5×). Class III obesity reduces life expectancy by 8-10 years. For Asians, obesity starts at BMI ≥ 27.5.

Can BMI be different for different ethnicities?

Yes! WHO recommends modified BMI cutoffs for Asian populations due to higher body fat percentage and health risks at lower BMIs. Asian cutoffs: Overweight ≥ 23 (vs 25), Obese ≥ 27.5 (vs 30). Studies show Asians develop type 2 diabetes at BMI 23-24, while Caucasians develop it at BMI 30+. Conversely, Pacific Islanders and Polynesians have lower health risks at higher BMIs due to greater muscle mass and bone density. Black populations have lower body fat at same BMI as white populations.

How can I lower my BMI safely?

Safe weight loss: 0.5-1 kg (1-2 lbs) per week through calorie deficit of 500-1,000 calories/day. Combine diet (reduce 300-500 calories) and exercise (burn 200-500 calories). To lose 1 BMI point (typically 2-3 kg), you need a deficit of 15,000-21,000 calories total (7,700 calories per kg fat). Focus on: whole foods, lean protein (1.6-2.2 g/kg body weight), vegetables, reduce processed foods and sugar. Exercise: 150-300 minutes moderate cardio weekly plus strength training 2-3×/week. Avoid crash diets (< 1,200 calories/day)—they cause muscle loss and metabolic slowdown. Consult doctor if BMI ≥ 35 or you have health conditions.

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

BMI is weight-to-height ratio (doesn't measure fat directly). Body fat percentage is actual proportion of fat mass to total body weight (measured by DEXA, bioelectrical impedance, or calipers). Two people with same BMI can have vastly different body fat: a muscular athlete with BMI 27 might have 12% body fat (healthy), while a sedentary person with BMI 27 might have 30% body fat (high risk). Healthy body fat: men 10-20% (athletes 6-13%), women 18-28% (athletes 14-20%). Body fat percentage is more accurate for health assessment but harder to measure than BMI.

Is BMI 25 overweight or normal?

BMI 25.0 is the threshold for 'overweight' category (25-29.9). However, BMI 25-27 is considered low-risk overweight—health risks are minimal compared to BMI 30+. Many health professionals consider BMI 23-27 acceptable for adults, especially those who exercise regularly. The key is body composition: BMI 25 with high muscle mass and low body fat is healthier than BMI 23 with low muscle and high fat. Focus on waist circumference (< 102 cm men, < 88 cm women) and fitness level rather than obsessing over BMI 24.9 vs 25.0.