BMI Calculator
Calculate your Body Mass Index (BMI), clinical weight classification, and healthy weight range for your height using official World Health Organization standards.
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المعادلة الرياضية
BMI = weight_kg / (height_m)² = (703 × weight_lb) / (height_in)² مثال توضيحي
For an adult standing 175 cm tall and weighing 70 kg, the calculated BMI is 22.9, falling inside the standard WHO Normal Weight category with a healthy range of 56.7 to 76.3 kg.
Understanding Body Mass Index (BMI)
Body Mass Index (BMI), originally developed in the 19th century by Belgian mathematician Adolphe Quetelet as the Quetelet Index, is the global epidemiological screening standard used by healthcare systems and international health authorities to categorize body mass relative to height.
While BMI is not a direct measure of body fat percentage, its strong statistical correlation with metabolic and cardiovascular risk makes it a primary clinical screening tool worldwide.
Mathematical Formulation
BMI is defined as an individual’s body mass divided by the square of their height:
Metric System:
BMI = Weight (kg) / [Height (m)]²
Imperial System:
BMI = (703 × Weight (lbs)) / [Height (inches)]²
Diagnostic Classification Thresholds
The World Health Organization (WHO) divides adult BMI scores into clinical categories:
| BMI Range (kg/m²) | WHO International Standard | Asian Population Standard |
|---|---|---|
| < 18.5 | Underweight | Underweight |
| 18.5 - 22.9 | Normal weight | Normal weight (Optimal) |
| 23.0 - 24.9 | Normal weight | Overweight (Increased risk) |
| 25.0 - 27.4 | Overweight (Pre-obese) | Overweight (High risk) |
| 27.5 - 29.9 | Overweight (Pre-obese) | Obese Class I |
| 30.0 - 34.9 | Obesity Class I (Moderate) | Obese Class I |
| 35.0 - 39.9 | Obesity Class II (Severe) | Obese Class II |
| ≥ 40.0 | Obesity Class III (Morbid) | Obese Class III |
Step-by-Step Worked Demonstration
Consider an adult measuring 175 cm (1.75 m) in height and weighing 70 kg:
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Calculate Height Squared: 1.75 × 1.75 = 3.0625 m²
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Compute BMI: BMI = 70 / 3.0625 ≈ 22.857 → 22.9 kg/m²
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Determine Healthy Weight Range (18.5 - 24.9): Minimum: 18.5 × 3.0625 = 56.7 kg (125.0 lbs) Maximum: 24.9 × 3.0625 = 76.3 kg (168.2 lbs)
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Assessment: At 22.9 kg/m², the score lies safely inside the normal weight bracket under both the WHO international scale and the Asian population guidelines (< 23.0).
Key Limitations of the BMI Metric
Although valuable for population studies, BMI exhibits well-documented individual diagnostic limitations:
- No Muscle vs. Fat Discrimination: A competitive sprinter and an inactive individual of identical height and weight have identical BMIs, despite vastly different body compositions.
- Fat Distribution Ignored: Visceral fat (stored within the abdominal cavity around internal organs) carries substantially higher cardiovascular risk than subcutaneous fat stored on the hips and thighs.
- Pediatric Inapplicability: Children and adolescents must be evaluated using pediatric growth charts (percentiles), as their body proportions change continuously during puberty.
To determine your daily energy balance, explore our calorie calculator or examine height-based clinical models using the ideal weight calculator.
الأسئلة الشائعة
What is considered a normal BMI for adults?
Under standard World Health Organization (WHO) guidelines, a BMI between 18.5 and 24.9 is considered normal or healthy weight. A BMI below 18.5 is underweight, 25.0 to 29.9 is overweight, and 30.0 or greater indicates obesity.
Why are different BMI cut-offs recommended for Asian populations?
Clinical research shows that populations of South Asian, East Asian, and Southeast Asian descent tend to accumulate higher percentages of visceral body fat at lower BMIs. Consequently, the WHO Expert Consultation established lower thresholds: Overweight at 23.0 and Obese at 27.5.
Can muscular athletes have an artificially high BMI?
Yes. BMI calculates total mass relative to height squared without differentiating skeletal muscle from adipose tissue. Heavily muscled bodybuilders, rugby players, and weightlifters often register as 'overweight' or 'obese' despite having sub-12% body fat.
What is BMI Prime?
BMI Prime is the ratio of your actual BMI to the upper boundary of the normal weight range (25.0). A BMI Prime under 0.74 is underweight, between 0.74 and 1.0 is normal, and above 1.0 indicates excess weight.
Is BMI accurate for elderly individuals?
In adults over 65 years, bone demineralization and age-related muscle loss (sarcopenia) occur. Geriatric medicine often considers a slightly higher BMI (23.0 to 27.0) protective against frailty and mortality.