BMI Calculator
Body Mass Index · WHO Standards
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Enter your height and weight to calculate your Body Mass Index.
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UnderweightNormalOverweightObese
UnderweightBelow 18.5
Normal weight18.5 – 24.9
Overweight25.0 – 29.9
Obese Class I30.0 – 34.9
Obese Class II35.0 – 39.9
Obese Class III40.0 and above
Healthy weight range for your height: -
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BMI Classification — WHO Standards
BMI (Body Mass Index) is a screening tool that estimates body fatness based on height and weight. The formula is: BMI = weight (kg) ÷ height (m)². For imperial units: BMI = (weight in lbs × 703) ÷ height in inches². The result is a single number that places you in a WHO classification category.
First developed by Belgian mathematician Adolphe Quetelet in 1830, BMI was adopted by the World Health Organization as a global standard for classifying weight status in populations. It remains the most widely used screening tool for weight-related health risks due to its simplicity and the extensive body of research correlating BMI with health outcomes.
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Increased |
| 18.5 – 24.9 | Normal weight | Low (lowest risk) |
| 25.0 – 29.9 | Overweight | Increased |
| 30.0 – 34.9 | Obese Class I | High |
| 35.0 – 39.9 | Obese Class II | Very High |
| 40.0 and above | Obese Class III | Extremely High |
BMI Limitations
BMI does not distinguish between muscle and fat. Athletes may have high BMI with low body fat. The elderly may have normal BMI but high body fat due to muscle loss. BMI also ignores fat distribution — visceral (abdominal) fat is more dangerous than subcutaneous fat at the same BMI.
Ethnicity Adjustments
WHO recognizes that Asian populations have higher metabolic risk at lower BMI thresholds. Many Asian health guidelines use 23.0 as the overweight threshold (vs 25.0) and 27.5 for obesity (vs 30.0). South Asian individuals in particular face increased cardiometabolic risk at BMIs below 25.
BMI vs Body Fat %
Body fat percentage is a more direct measure of adiposity. Healthy ranges: men 10-20%, women 18-28% (fitness). BMI and body fat correlate moderately (r ≈ 0.7) but diverge significantly for muscular individuals. DEXA scans, hydrostatic weighing, and bioelectrical impedance provide more accurate body composition data.
Waist Circumference
WHO recommends using waist circumference alongside BMI. High risk: men >102 cm (40 in), women >88 cm (35 in). Waist-to-height ratio (WHtR) >0.5 indicates elevated risk regardless of BMI category. Abdominal fat is a stronger predictor of cardiovascular disease and type 2 diabetes than BMI alone.
BMI is a general population screening tool, not a medical diagnosis. Always consult a healthcare professional for a complete assessment of your health status.
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Frequently Asked Questions
What is a healthy BMI range for adults?+
According to WHO guidelines, a BMI of 18.5 to 24.9 is considered the healthy (normal weight) range for most adults. Below 18.5 is underweight, 25.0 to 29.9 is overweight, and 30.0 or above is classified as obese. The normal weight range is associated with the lowest risk of weight-related health conditions. Note that these thresholds may be lower for Asian populations — some guidelines use 23.0 as the overweight threshold for people of Asian descent.
How do I calculate BMI manually?+
Metric formula: BMI = weight in kg divided by height in metres squared. Example: 70 kg ÷ (1.75 m × 1.75 m) = 70 ÷ 3.0625 = 22.9. Imperial formula: BMI = (weight in pounds × 703) divided by height in inches squared. Example: (160 lbs × 703) ÷ (69 inches × 69 inches) = 112,480 ÷ 4,761 = 23.6. Both calculations give the same result when units are converted correctly.
Is BMI accurate for athletes and muscular people?+
No. BMI is notoriously inaccurate for highly muscular individuals. Since muscle is denser than fat, a bodybuilder or elite athlete may have a BMI in the overweight or obese range despite very low body fat percentage. The NFL has players classified as "obese" by BMI who have body fat percentages below 15%. For muscular individuals, body fat percentage measurement (DEXA, underwater weighing, or skinfold calipers) is a far more meaningful assessment of weight-related health risk.
What BMI is considered obese?+
A BMI of 30.0 or above is classified as obese. Obesity is subdivided into three classes: Class I (30.0-34.9), associated with high health risk; Class II (35.0-39.9), associated with very high risk; and Class III or "severe obesity" (40.0 and above), associated with extremely high risk. Obesity is associated with significantly increased risk of type 2 diabetes, cardiovascular disease, hypertension, sleep apnoea, osteoarthritis, and certain cancers.
Does BMI differ for men and women?+
The standard BMI formula and WHO classification thresholds are identical for men and women. However, women naturally carry 6-11 percentage points more body fat than men at the same BMI due to biological differences (reproductive hormones, breast tissue). This means women at the same BMI may have more body fat than men. Some researchers have proposed gender-specific thresholds, but WHO and most clinical guidelines currently use a single standard for both sexes.
What is a healthy BMI for older adults?+
The standard BMI thresholds apply to adults 20-65, but research suggests older adults (65+) may benefit from a slightly higher BMI. A BMI of 25-27 may actually be protective in older adults because it provides reserves against illness and muscle wasting (sarcopenia). Some gerontology guidelines suggest 22-27 as a preferable range for people over 65. Being underweight (BMI below 22) in older adults is associated with higher mortality risk than mild overweight.
How is BMI different for children and teenagers?+
Children and adolescents (ages 2-19) use BMI-for-age percentiles rather than fixed thresholds. The CDC provides separate growth charts for boys and girls. Underweight: below the 5th percentile. Healthy weight: 5th to 84th percentile. Overweight: 85th to 94th percentile. Obese: 95th percentile or above. This percentile-based system accounts for normal changes in body composition as children grow and develop. This calculator is designed for adults; a pediatrician should assess children's growth.
What is the relationship between BMI and health risks?+
BMI correlates with health risks at the population level, though the relationship is not perfectly linear. A BMI in the normal range (18.5-24.9) is associated with the lowest overall mortality risk. Both underweight and obesity carry elevated risks, but for different reasons. Underweight is associated with malnutrition, immune dysfunction, bone loss, and increased infection risk. Overweight and obesity are associated with metabolic syndrome, cardiovascular disease, type 2 diabetes, joint problems, and certain cancers. However, the BMI-mortality relationship forms a "J-curve" — very low BMI carries significant risk, as does very high BMI.
What should I do if my BMI indicates I am overweight or obese?+
A BMI above 25 is not a diagnosis — it is a signal to discuss health with your doctor. Your physician can evaluate your full clinical picture including waist circumference, blood pressure, blood sugar, cholesterol, family history, and lifestyle factors. Not everyone with a high BMI needs the same intervention. Some people with BMI 25-30 have no metabolic abnormalities ("metabolically healthy overweight"). Your doctor may recommend dietary changes, increased physical activity, behavioural support, or other interventions based on your complete health profile.
Can BMI be used to diagnose obesity or other conditions?+
No. BMI is a screening tool, not a diagnostic tool. According to the CDC and WHO, a high BMI indicates the need for further evaluation but does not diagnose obesity or any disease. For clinical diagnosis, healthcare providers consider BMI alongside body fat percentage, fat distribution, metabolic markers (blood glucose, cholesterol, triglycerides), blood pressure, and overall health history. A person can be obese by BMI but metabolically healthy, or be within normal BMI range but have significant metabolic dysfunction. Always interpret BMI in clinical context.