⚖️ WHO & CDC Standards · Adult BMI · Ideal Weight · Health Risk Assessment
BMI Calculator — Body Mass Index & Health Risk Estimator
Calculate your Body Mass Index (BMI) instantly in metric or US units. Get your WHO/CDC classification, ideal weight range for your height, health risk assessment, and an EMR-ready report. Supports both standard and Asian BMI thresholds.
Educational tool only. BMI is a screening measure, not a diagnosis — it doesn't directly measure body fat or account for muscle mass, fat distribution, age, or ethnicity on its own. Use this alongside other health markers, and talk to a clinician before making decisions about weight, diet, or exercise based on this result.
Lowest mortality risk range. Associated with optimal metabolic health.
25.0–29.9
Overweight
Moderate
Increased risk of hypertension, dyslipidemia, sleep apnea, type 2 diabetes
30.0–34.9
Obese — Class I
High
Significantly elevated cardiovascular, metabolic, and joint disease risk
35.0–39.9
Obese — Class II
Very High
Major risk for type 2 diabetes, coronary artery disease, stroke, and sleep apnea
40.0 and above
Severely Obese — Class III
Extremely High
Highest risk for all obesity-related comorbidities. Bariatric surgery may be indicated.
Source: World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) adult BMI classification standards. See References below.
BMI Classification for Asian Adults — WHO Lower Thresholds
BMI Range (kg/m²)
Classification
Below 18.5
Underweight
18.5–22.9
Normal Weight
23.0–24.9
At Risk
25.0–27.4
Overweight
27.5 and above
Obese
Asian populations, on average, carry proportionally more visceral fat at lower BMI levels. WHO recommends overweight classification at BMI ≥23.0 and obese at ≥27.5 for Asian adults (WHO Expert Consultation, 2004 — see References).
Waist Circumference — Cardiometabolic Risk Guide
Population Group
Low Risk
Increased Risk
Substantially Increased Risk
Men
< 94 cm (37 in)
94–102 cm (37–40 in)
> 102 cm (40 in)
Women
< 80 cm (31.5 in)
80–88 cm (31.5–35 in)
> 88 cm (35 in)
Asian Men
< 90 cm (35 in)
≥ 90 cm (35 in)
≥ 90 cm (35 in)
Asian Women
< 80 cm (31.5 in)
≥ 80 cm (31.5 in)
≥ 80 cm (31.5 in)
Waist circumference is used alongside BMI as part of metabolic syndrome risk criteria (Alberti et al., 2009 — see References).
What Is BMI?
A patient walks into a clinic for a routine check-up. Before any blood is drawn, the nurse records two numbers — height and weight — and calculates a single figure that will appear on the chart for the rest of the visit: BMI.
Body Mass Index (BMI) is a simple screening tool that estimates body fatness from height and weight, developed by Belgian mathematician Adolphe Quetelet in the 1830s and later adopted by the World Health Organization as a global obesity screening standard.
The formula is straightforward: BMI = Weight (kg) ÷ Height (m)², or in US units: BMI = (Weight in lbs × 703) ÷ Height in inches². A BMI of 18.5-24.9 is classified as normal weight; 25-29.9 as overweight; 30 and above as obese.
How to Interpret Your Results
The result above gives you three things together, not just one number: your BMI, its WHO/CDC category, and an ideal weight range for your height. Look at all three, not the number alone — a BMI just above a category boundary (say, 25.2 vs. 24.8) does not represent a meaningfully different health status, while the category itself is a useful shorthand for where you sit relative to population risk data.
If you selected Asian thresholds, note that the category boundaries shift lower (overweight from 23.0, not 25.0) because of the different fat-distribution and disease-risk pattern described in the research below.
Ideal Weight Based on BMI — How It's Calculated
Your ideal weight range is calculated by reverse-engineering the normal BMI range (18.5-24.9) for your specific height: minimum ideal weight (kg) = 18.5 × height (m)²; maximum ideal weight (kg) = 24.9 × height (m)².
For a person 170 cm (1.70 m) tall: minimum = 18.5 × 2.89 = 53.5 kg (117.8 lbs); maximum = 24.9 × 2.89 = 71.9 kg (158.6 lbs).
This range is a population-level statistical estimate — athletes, older adults, and pregnant individuals in particular should interpret it with caution rather than as a personal target.
BMI Limitations — Why It's Not the Whole Picture
Doesn't measure body fat directly: BMI can't distinguish a pound of muscle from a pound of fat — a muscular athlete and a sedentary person at the same weight and height will have the same BMI despite very different health profiles.
Ignores fat distribution: Abdominal (visceral) fat around the organs carries more cardiometabolic risk than fat stored elsewhere. Two people with the same BMI can have different risk depending on where they store fat — which is why the waist circumference table above exists as a complement, not a replacement.
Ethnicity differences: Asian populations tend to carry more visceral fat at a given BMI than Caucasian populations, which is the basis for the WHO's lower Asian thresholds.
Age effects: BMI doesn't account for sarcopenia (age-related muscle loss) — an older adult with reduced muscle mass may show a "normal" BMI alongside a higher body fat percentage.
Better alternatives for individual assessment: waist circumference, waist-to-hip ratio, DEXA body composition scans, and body fat percentage.
Clinical Significance
Large cohort studies show a J- or U-shaped relationship between BMI and mortality, with risk elevated at both extremes. In the NIH-AARP Diet and Health Study — a prospective cohort of roughly 500,000 US adults — Adams et al. (2006) found the lowest mortality risk among healthy never-smokers at a BMI of about 22.5-24.9, with progressively higher risk at both higher and lower BMI. Obesity (BMI ≥30) is associated with meaningfully elevated risk of type 2 diabetes, hypertension, and coronary artery disease across the epidemiological literature, though the exact size of that increase varies by study population and design. Below BMI 18.5, malnutrition, immune dysfunction, and reduced bone density become more common concerns.
When to Use This Calculator
Use this tool as a quick screening check on your weight relative to population health data, or to track BMI changes over time alongside other health markers. It's a reasonable starting point for a conversation with a healthcare provider, not a stand-in for one.
Don't rely on BMI alone if you're an athlete with high muscle mass, pregnant, elderly with reduced muscle mass, or if you have a known condition affecting body composition — in those cases, waist circumference, body composition testing, or a clinician's assessment will give a more accurate picture than BMI by itself.
About This Calculator's Basis
This calculator applies the standard WHO/CDC BMI formula and classification thresholds, plus the WHO's separate lower thresholds for Asian populations, referenced below. The ideal-weight-range figure is a simple algebraic reverse-calculation of the normal BMI band for a given height — a common convention, not a distinct clinical formula of its own.
Medical disclaimer: This calculator is for general educational and screening purposes only. It does not diagnose any medical condition and does not account for individual factors such as muscle mass, pregnancy, or specific health conditions that can affect how BMI should be interpreted for a given person. Consult a licensed healthcare provider for personalized guidance on weight, nutrition, or exercise.
Adams KF, Schatzkin A, Harris TB, et al. Overweight, obesity, and mortality in a large prospective cohort of persons 50 to 71 years old. N Engl J Med. 2006;355(8):763-778. doi:10.1056/NEJMoa055643. PMID 16926275.
WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet. 2004;363(9403):157-163. doi:10.1016/S0140-6736(03)15268-3.
Alberti KGMM, Eckel RH, Grundy SM, et al. Harmonizing the metabolic syndrome: a joint interim statement. Circulation. 2009;120(16):1640-1645. doi:10.1161/CIRCULATIONAHA.109.192644. PMID 19805654.
Frequently Asked Questions
What is a good BMI for a woman?
The WHO and CDC use the same BMI classification for all adults regardless of sex: normal (healthy) weight is BMI 18.5-24.9. Women tend to carry more body fat than men at the same BMI, which is normal and physiologically appropriate for reproductive function; this also means BMI-based cardiovascular risk estimates can differ somewhat by sex at equivalent BMI. Asian women should use the lower WHO Asian thresholds: normal BMI 18.5-22.9; overweight at 23.0 or above.
Can you have a normal BMI but still be unhealthy?
Yes. This is sometimes called "normal weight obesity" or "skinny fat" — a BMI in the normal range combined with a high body fat percentage and low muscle mass, which some research links to insulin resistance and elevated cardiovascular risk despite a "normal" BMI. The reverse also occurs: some people with a higher BMI have normal metabolic markers, though research suggests this tends to be a transient state for many. The takeaway is that BMI alone is not sufficient to assess health — it's best combined with blood pressure, blood glucose, cholesterol, waist circumference, and fitness level.
How much do I need to lose to reach a healthy BMI?
Enter your height in the calculator above to see your ideal weight range. The difference between your current weight and the top of the normal BMI range (24.9) is the weight change needed to reach that range. For context, losing even 5-10% of body weight, without necessarily reaching a "normal" BMI, is associated with meaningful improvements in blood pressure, insulin resistance, and cardiovascular risk markers in the research literature. A commonly recommended, sustainable pace is about 0.5-1.0 kg (1-2 lbs) per week. Talk to a healthcare provider or registered dietitian before starting a weight-loss program.
Is BMI different for children and teenagers?
Yes. BMI for children and adolescents (ages 2-19) is age- and sex-specific, expressed as a BMI-for-age percentile rather than a fixed category, because body composition changes substantially during development. Roughly: below the 5th percentile is underweight; 5th-84th percentile is healthy weight; 85th-94th percentile is overweight; 95th percentile or above is obese. This calculator is designed for adults (18+) only — for children, use the CDC's age- and sex-specific BMI-for-age growth charts.
Is BMI accurate for everyone?
No — BMI has well-documented limitations. It doesn't distinguish muscle from fat, so athletes and bodybuilders are sometimes classified as overweight or obese despite low body fat. It doesn't account for fat distribution — abdominal (visceral) fat carries more cardiometabolic risk than fat elsewhere on the body. It can underestimate risk in some Asian populations, who tend to carry more visceral fat at a given BMI, and may not fully capture risk in older adults who have lost muscle mass with age. Waist circumference, waist-to-hip ratio, DEXA body composition scans, and body fat percentage are commonly used alongside or instead of BMI for a fuller picture.