Calculate your Body Mass Index to check if your weight is healthy for your height.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obese (Class I) |
| 35.0 – 39.9 | Obese (Class II) |
| 40.0 and above | Obese (Class III) |
BMI (Body Mass Index) is calculated by dividing your weight in kilograms by the square of your height in meters:
BMI = weight (kg) / height (m)²
BMI is a simple screening tool used by healthcare professionals worldwide. While it does not directly measure body fat, it correlates with more direct measures of body fat and helps identify potential weight-related health risks.
Body Mass Index, or BMI, is a numerical value derived from your weight and height that provides a quick screening measure for body weight categories. Developed by Belgian mathematician Adolphe Quetelet in the 1830s, it remains one of the most widely used tools by healthcare providers to assess whether a person falls within a healthy weight range. BMI does not measure body fat directly; instead, it uses a simple formula to estimate whether your weight is proportionate to your height. The World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) both endorse BMI as a practical first-step indicator for potential weight-related health risks, including heart disease, type 2 diabetes, and hypertension. While BMI has limitations—it cannot distinguish between lean muscle mass and fat, and it may not be equally accurate across all ethnic groups, ages, or fitness levels—it is valuable as a population-level screening tool and a starting point for individual health conversations.
BMI is calculated using a straightforward formula. Here is how to do it step by step:
Metric formula: BMI = weight (kg) ÷ height (m)2
Imperial formula: BMI = [weight (lbs) ÷ height (in)2] × 703
Worked example (metric): A person weighs 75 kg and is 1.78 m tall.
Worked example (imperial): A person weighs 165 lbs and is 5’10” (70 inches).
| Height | Healthy Weight (BMI 18.5–24.9) |
|---|---|
| 5’0” (152 cm) | 97 – 128 lbs (44 – 58 kg) |
| 5’1” (155 cm) | 100 – 132 lbs (45 – 60 kg) |
| 5’2” (157 cm) | 104 – 136 lbs (47 – 62 kg) |
| 5’3” (160 cm) | 107 – 141 lbs (49 – 64 kg) |
| 5’4” (163 cm) | 110 – 145 lbs (50 – 66 kg) |
| 5’5” (165 cm) | 114 – 150 lbs (52 – 68 kg) |
| 5’6” (168 cm) | 118 – 155 lbs (54 – 70 kg) |
| 5’7” (170 cm) | 121 – 159 lbs (55 – 72 kg) |
| 5’8” (173 cm) | 125 – 164 lbs (57 – 74 kg) |
| 5’9” (175 cm) | 128 – 169 lbs (58 – 77 kg) |
| 5’10” (178 cm) | 132 – 174 lbs (60 – 79 kg) |
| 5’11” (180 cm) | 136 – 179 lbs (62 – 81 kg) |
| 6’0” (183 cm) | 140 – 184 lbs (64 – 83 kg) |
| 6’1” (185 cm) | 144 – 189 lbs (65 – 86 kg) |
| 6’2” (188 cm) | 148 – 194 lbs (67 – 88 kg) |
| 6’3” (191 cm) | 152 – 200 lbs (69 – 91 kg) |
| 6’4” (193 cm) | 156 – 205 lbs (71 – 93 kg) |
BMI can overestimate body fat in athletes and bodybuilders who have high muscle mass. Muscle weighs more than fat per unit of volume, so a muscular person may register as overweight or obese by BMI despite having a low body-fat percentage. For these individuals, body-fat percentage measurements such as DEXA scans or skinfold calipers provide a more accurate assessment.
The World Health Organization classifies a BMI between 18.5 and 24.9 as normal weight. Below 18.5 is considered underweight, 25.0 to 29.9 is overweight, and 30.0 or above is classified as obese. These ranges apply to adults aged 20 and older regardless of gender.
For adults, the same BMI ranges apply to both men and women. However, for children and teenagers (ages 2 to 19), BMI is interpreted using age-and-sex-specific percentiles because body composition changes as children grow. An adult BMI chart should not be used for children.
Research shows that BMI correlates with health risks at a population level. Higher BMIs are associated with increased risk of cardiovascular disease, type 2 diabetes, certain cancers, and sleep apnea. However, individual risk also depends on factors like waist circumference, family history, diet, and physical activity.
A BMI of 40 or above is classified as Class III obesity, sometimes called morbid or severe obesity. A BMI between 35 and 39.9 with obesity-related health conditions may also be considered in this category for treatment purposes.
For most adults, checking BMI once or twice a year during routine medical checkups is sufficient. If you are actively trying to lose or gain weight, monthly checks can help track progress, but daily fluctuations in weight are normal and should not cause concern.
No. BMI is a ratio of weight to height, while body fat percentage measures the actual proportion of fat tissue in your body. Two people can have the same BMI but very different body-fat percentages depending on their muscle mass, bone density, and overall body composition.
BMI does not account for muscle mass, bone density, age, sex, ethnicity, or fat distribution. It may underestimate body fat in older adults who have lost muscle mass and overestimate it in athletes. Waist-to-hip ratio and body-fat percentage are useful complementary measurements.
Body Mass Index is a numerical measure that has been used since the 1830s to assess weight relative to height. Belgian mathematician Adolphe Quetelet developed the formula as part of his work on "social physics," seeking to define the characteristics of the average person. Originally called the Quetelet Index, it was renamed BMI in 1972 by physiologist Ancel Keys. Today, BMI is endorsed by the World Health Organization, the CDC, and virtually every national health agency as a first-step screening tool for weight-related health risks.
BMI matters because extensive research links higher BMI levels to increased risk of type 2 diabetes, cardiovascular disease, hypertension, sleep apnea, osteoarthritis, and certain cancers. Conversely, a very low BMI is associated with malnutrition, weakened immune function, osteoporosis, and fertility issues. While BMI alone cannot diagnose any condition, it flags potential concerns that warrant further evaluation through body fat measurements, waist circumference, blood tests, and clinical assessment.
The simplicity of BMI is both its greatest strength and its most significant limitation. It requires only height and weight, making it accessible to anyone. However, it cannot distinguish between muscle and fat mass, account for fat distribution, or adjust for age, sex, or ethnicity. A bodybuilder with 8% body fat may have a BMI of 30 (classified as obese), while an older adult with muscle loss could have a "normal" BMI despite carrying excess fat. For these reasons, BMI should be a starting point for health assessment, not the final word.
Despite limitations, BMI remains the most widely used tool because it is free, quick, non-invasive, and strongly correlated with direct measures of body fat at the population level. When combined with waist circumference (healthy: under 40 inches for men, under 35 for women), it provides a reasonably accurate picture of weight-related health risk for most adults.
Method 1 -- Metric formula: BMI = weight (kg) / height (m)^2. Example: 82 kg, 1.75 m. BMI = 82 / (1.75 x 1.75) = 82 / 3.0625 = 26.8 (overweight).
Method 2 -- Imperial formula: BMI = (weight (lbs) / height (in)^2) x 703. Example: 180 lbs, 5'10" (70 in). BMI = (180 / 4900) x 703 = 25.8 (overweight).
Method 3 -- Use this calculator: Enter height and weight in either metric or imperial units, click Calculate BMI, and instantly see your BMI value, category, and healthy weight range.
Common mistake: Forgetting to convert height to meters. If you enter centimeters directly (175 instead of 1.75), you get an absurdly small number. Always divide cm by 100 first, or use this calculator which handles the conversion automatically.
College athlete: A 22-year-old football player weighing 220 lbs at 6'0" has BMI 29.8 (nearly obese by BMI). However, with 12% body fat by DEXA scan, he is extremely fit. BMI fails because muscle weighs more than fat per unit volume.
Average adult male: A 35-year-old, 5'9", 170 lbs. BMI = 25.1, just barely overweight. Losing 5-10 lbs brings him into the normal range. Small changes like walking 30 minutes daily make a meaningful difference at this BMI.
Average adult female: A 30-year-old, 5'5", 140 lbs. BMI = 23.3, solidly normal weight. Healthy range for this height: 114-150 lbs (52-68 kg).
Older adult: A 70-year-old woman, 5'3", 125 lbs. BMI = 22.3. Some research suggests slightly higher BMIs (23-27) may be protective in older adults, providing reserves during illness.
Pregnant woman: BMI should use pre-pregnancy weight. A woman 140 lbs at 5'6" before pregnancy has pre-pregnancy BMI of 22.6. Healthy weight gain: 25-35 lbs for normal-weight women, 15-25 lbs for overweight, 11-20 lbs for obese women.
Teenager: For ages 2-19, BMI is plotted on age-and-sex-specific growth charts. A 14-year-old girl with BMI 22 might be at the 75th percentile (healthy), while the same BMI in a 10-year-old could indicate overweight.
Asian populations: Research shows Asian populations develop health risks at lower BMIs. WHO recommends overweight begins at BMI 23 (not 25) and obesity at 27.5 (not 30) for Asian adults.
Very tall person: A 6'6" man at 220 lbs has BMI 25.5. BMI tends to overestimate body fat in tall people and underestimate in short people. The Ponderal Index attempts to correct for this but is not widely used.
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 16.0 | Severe underweight | Very high risk of malnutrition |
| 16.0 - 16.9 | Moderate underweight | High risk |
| 17.0 - 18.4 | Mild underweight | Moderate risk |
| 18.5 - 24.9 | Normal weight | Lowest health risk |
| 25.0 - 29.9 | Overweight | Increased risk |
| 30.0 - 34.9 | Obese Class I | High risk |
| 35.0 - 39.9 | Obese Class II | Very high risk |
| 40.0+ | Obese Class III | Extremely high risk |
Healthcare: Doctors use BMI as an initial screening tool during routine checkups. A high BMI triggers further assessment including waist circumference, blood pressure, blood glucose, and cholesterol. BMI determines eligibility for weight loss medications and bariatric surgery (typically BMI 35+ with comorbidities or 40+).
Insurance: Life insurance companies use BMI to set premiums. Applicants with overweight or obese BMIs may pay 20-50% more. Some health insurance plans offer wellness discounts for maintaining a healthy BMI.
Military and law enforcement: Military branches have maximum weight and body fat standards. The US Army uses BMI as an initial screen, with tape measurements for body fat if limits are exceeded.
Sports and fitness: Athletes often have BMIs that misrepresent fitness. A marathon runner might have BMI 20 with 7% body fat, while a rugby player has BMI 31 with 15% body fat. Sports medicine prefers DEXA scans or skinfold measurements.
Public health: BMI data helps governments track obesity trends and design interventions. Global obesity has nearly tripled since 1975, with over 1.9 billion adults classified as overweight.
Focus on body composition, not just BMI. Strength training increases muscle mass, which raises metabolic rate and improves health markers even if your BMI number does not change dramatically. A person with more muscle at BMI 26 is often healthier than someone with less muscle at BMI 23.
The BMI formula was never intended to measure individual health. Quetelet created it in 1832 to study population trends. It became a clinical tool out of convenience. The AMA recommended in 2023 that BMI should be used alongside other measures, not alone.
Sustainable weight management: Aim to lose no more than 1-2 lbs per week through a moderate caloric deficit of 500-750 calories per day. Combine dietary changes with 150+ minutes of moderate aerobic activity per week plus 2 strength training sessions. Crash diets lead to muscle loss and metabolic slowdown.
Track trends, not single measurements: Weight fluctuates daily due to hydration, food intake, and hormones. Weigh yourself at the same time each day and track the weekly average. A downward trend over 4-8 weeks is more meaningful than any single reading.
Oxford mathematician Nick Trefethen proposed BMI = 1.3 x weight(kg) / height(m)^2.5 in 2013. This reduces bias for very short and tall people but has not been widely adopted because traditional BMI has decades of epidemiological research behind it.
Waist-to-hip ratio (WHR) measures fat distribution. A WHR above 0.90 for men or 0.85 for women indicates central obesity with higher cardiovascular risk regardless of BMI. Many professionals now recommend using both BMI and WHR together.
Meta-analyses suggest lowest all-cause mortality at BMI 22-25 for adults under 65. For those over 65, slightly higher BMI of 23-27 appears optimal. Extreme BMIs in either direction are associated with significantly higher mortality risk.
A BMI of 25 corresponds to roughly 20-25% body fat in men and 30-35% in women, but individual variation is substantial. Two people with the same BMI can have body fat percentages differing by 10+ points depending on muscle mass, age, and genetics.
Use pre-pregnancy weight for BMI. Pregnancy weight gain is expected and necessary. Pre-pregnancy BMI determines appropriate weight gain targets. Tracking weight gain during pregnancy is more useful than recalculating BMI.
Body fat percentage (via DEXA scan) is the gold standard. Waist circumference and waist-to-hip ratio assess fat distribution. Newer metrics like Body Roundness Index (BRI) and Relative Fat Mass (RFM) are gaining research support. Combining BMI with waist circumference provides the best practical balance.
Only through height changes. Children experience BMI changes as they grow. Older adults may see BMI decrease from height loss due to spinal compression. Body recomposition (gaining muscle while losing fat) can maintain the same BMI while dramatically improving health markers.
Body fat percentage: Measures the actual proportion of fat in your body. Healthy ranges: 10-20% for men, 18-28% for women. Unlike BMI, it distinguishes lean mass from fat. Use the Body Fat Calculator.
TDEE: Total calories your body burns per day including exercise. Knowing your TDEE helps create a caloric deficit for weight loss or surplus for muscle gain. Use the TDEE Calculator.
Ideal weight: Various formulas estimate ideal weight based on height and frame size. These give a target range aligned with BMI 20-25. Use the Ideal Weight Calculator.
Daily calorie needs: The Mifflin-St Jeor equation estimates your BMR, adjusted for activity level to determine maintenance calories. Use the Calorie Calculator.