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Your Results
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Fill in your details and tap Calculate My BMI to see your personalised body mass index, body fat index estimate, and healthy weight range instantly.
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kg/m²
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UnderweightNormalOverweightObese
BMI Prime
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Below 1.00 = healthy
Ponderal Index
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Normal: 11–15 kg/m³
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Healthy Weight Range for Your Height
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BMI and body fat index estimates are screening tools, not a clinical diagnosis. Consult a healthcare professional for a full assessment.
Height–Weight BMI Chart
Your position on the body mass index chart for your height.
UnderweightNormalOverweightObese IObese II+
Understanding Body Mass Index & Body Fat Index
Body Mass Index (BMI) is the world's most widely used healthy body weight calculator metric, trusted by the WHO, CDC, and health professionals in over 190 countries.
It gives a quick, evidence-backed estimate of whether your weight is proportionate to your height — a key indicator for body mass index obesity risk screening.
Alongside BMI, this page also covers the body fat index concept, BMI Prime, and the Ponderal Index, so you get the most complete picture possible without needing expensive lab tests.
What is Body Mass Index?
Body Mass Index (BMI) is a numerical value derived from your weight and height. Developed by mathematician Adolphe Quetelet in the 1830s, it serves as the global standard first-step screening tool for identifying whether a person is underweight, at a healthy body weight, overweight, or in a category associated with body mass index obesity.
BMI is used by doctors, dietitians, public health researchers, and insurers worldwide. It is neither a direct measure of body fat nor a diagnostic test, but it correlates reliably with body fat percentage for roughly 90–95% of the general adult population.
How is BMI Calculated?
Metric Formula
BMI = weight (kg) ÷ height² (m)
Example: 73 kg ÷ (1.78 m)² = 23.0 kg/m²
US / Imperial Formula
BMI = 703 × weight (lbs) ÷ height² (in)
Example: 703 × 160 ÷ (70 in)² = 22.9 kg/m²
The factor 703 is a unit conversion constant. Our healthy body weight calculator handles both formulas automatically — just pick your preferred units.
WHO BMI Classification (Adults 20+)
Classification
BMI Range (kg/m²)
Severe Thinness
Below 16.0
Moderate Thinness
16.0 – 16.9
Mild Thinness
17.0 – 18.4
Normal Weight
18.5 – 24.9
Overweight
25.0 – 29.9
Obese Class I
30.0 – 34.9
Obese Class II
35.0 – 39.9
Obese Class III
40.0 and above
These thresholds are defined by the World Health Organization and are the basis for global body mass index obesity surveillance. For children and teens, the CDC uses age- and sex-specific percentile charts instead.
What the Categories Mean
Underweight (below 18.5): May signal inadequate caloric intake or an underlying condition. Risks include malnutrition, bone loss, weakened immunity, and hormonal disruption.
Normal / Healthy Body Weight (18.5–24.9): Associated with the lowest risk of weight-related chronic disease. This is the target range our healthy body weight calculator displays for your specific height.
Overweight (25–29.9): Elevated risk of cardiovascular disease and type 2 diabetes. A 5–10% weight reduction can meaningfully reduce risk.
Body Mass Index Obesity (30+): Substantially raised risk across a wide range of chronic conditions. Medical guidance is strongly recommended. Even small sustained lifestyle changes produce real health gains.
Body Fat Index — What's the Difference?
The term body fat index (sometimes used interchangeably with body fat percentage or body adiposity index) refers to the proportion of your total body mass that is fat tissue. Unlike BMI, it directly measures fat — but requires specialist equipment such as a DEXA scanner, bioelectrical impedance device, or skinfold calipers.
Healthy body fat percentage ranges (approximate):
Men: 6–24% (athletes 6–13%, fit 14–17%, average 18–24%)
Women: 16–30% (athletes 16–20%, fit 21–24%, average 25–31%)
BMI and the body fat index are complementary tools. BMI is free, fast, and accessible; body fat percentage is more precise but requires measurement. Use both together for the best picture.
BMI Prime & Ponderal Index Explained
BMI Prime is simply your BMI divided by 25 — expressing how close you are to the upper healthy limit as a ratio. A BMI Prime of exactly 1.00 means a BMI of 25; below 1.00 is healthy; above 1.00 means overweight or obese. It lets you compare across populations without needing to remember cutoff numbers.
BMI Prime Formula
BMI Prime = BMI ÷ 25
Example: BMI 23.0 ÷ 25 = 0.92 (healthy)
Ponderal Index (PI) divides weight by height cubed (kg/m³), making it less sensitive to height extremes than BMI — particularly useful for very tall or very short individuals.
Ponderal Index Formula
PI = weight (kg) ÷ height³ (m)
Normal adult range: 11 – 15 kg/m³
Limitations of BMI as a Healthy Body Weight Calculator
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Athletes & Muscle
Muscle is denser than fat. Athletes may show "overweight" BMI with excellent body fat index scores. A bodybuilder with 8% body fat may have BMI 28 — technically overweight by this metric alone.
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Age & Sarcopenia
Older adults lose muscle and gain fat with age. A "normal" BMI in a 70-year-old may conceal sarcopenic obesity — high body fat index despite acceptable weight.
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Ethnicity
Asian populations face higher metabolic risk at lower BMI values. WHO recommends overweight threshold of ≥23 kg/m² for East and South Asian adults.
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Sex Differences
Women naturally carry more body fat than men at the same BMI. The same BMI value reflects different body fat index levels across biological sexes.
Frequently Asked Questions
What is a healthy BMI for adults?
The WHO defines a healthy body weight as a BMI between 18.5 and 24.9 kg/m² for adults aged 20+. If you are of Asian descent, your doctor may use lower thresholds (overweight ≥23, obese ≥27.5). Our healthy body weight calculator shows you the exact weight range for your height that falls in the normal category.
What is the difference between body fat index and BMI?
BMI (body mass index) is derived from height and weight alone — it is a proxy measure. The body fat index or body fat percentage directly measures how much of your body is fat tissue. BMI is free and instant; body fat index requires a DEXA scan, BIA scale, or calipers. For most people BMI correlates well with body fat, but athletes and older adults may see discrepancies between the two.
At what BMI does obesity begin?
According to the WHO, body mass index obesity is defined as a BMI of 30 kg/m² or above. This is subdivided into Class I (30–34.9), Class II (35–39.9), and Class III — sometimes called severe or morbid obesity — at 40 and above. Each class carries progressively greater risks of type 2 diabetes, cardiovascular disease, and other chronic conditions.
How accurate is BMI for children?
For children and teenagers aged 2–20, the CDC recommends BMI-for-age percentile charts rather than fixed adult cutoffs. Underweight is below the 5th percentile; healthy weight is 5th to below 85th; at-risk is 85th to below 95th; and overweight/obese is at or above 95th. This calculator uses adult WHO thresholds — for children, consult a paediatrician or use the CDC's dedicated child BMI tool.
How often should I recalculate my BMI?
For most adults, recalculating every 1–3 months is enough to see meaningful trends. Daily fluctuations in body weight (hydration, food volume, hormonal cycles) don't reflect true fat changes. Always weigh yourself at the same time of day, in the same clothing, on the same scale for reliable data.
Medical Disclaimer: The BMI calculator, body fat index estimates, and healthy body weight calculator results on this page are for educational purposes only. They do not constitute medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider regarding your health, weight management, or body mass index obesity concerns.
