What Is BMI?
Body Mass Index (BMI) is a widely used screening measurement that estimates whether a person has a healthy body weight relative to their height. Originally developed by the Belgian mathematician Adolphe Quetelet in the 19th century, BMI is now recommended by the World Health Organization (WHO) as a primary tool for assessing population-level weight status and individual health risk.
BMI is calculated by dividing your weight in kilograms by the square of your height in metres. The result is compared against established categories — underweight, normal, overweight, or obese — to identify potential health risks. While BMI does not directly measure body fat percentage, research consistently shows strong correlations between BMI and metabolic disease risk, cardiovascular disease, and overall mortality in large population studies.
For adults aged 20 and over, BMI interpretation uses the same fixed thresholds regardless of age or sex. For children and teenagers, age- and sex-specific BMI percentile charts are used instead of the adult scale. Pregnant women should use pre-pregnancy weight for BMI calculation and consult their healthcare provider for guidance.
BMI Formula & Examples
Metric Formula
Example: Weight 72 kg, Height 175 cm (1.75 m)
BMI = 72 ÷ (1.75 × 1.75) = 72 ÷ 3.0625 = 23.5 → Normal weight
Imperial Formula
Example: Weight 160 lbs, Height 5 ft 9 in (69 inches)
BMI = 703 × 160 ÷ (69 × 69) = 112,480 ÷ 4,761 = 23.6 → Normal weight
WHO BMI Categories 2026
| BMI Range | Category | Health Risk Level |
|---|---|---|
| Below 18.5 | Underweight | Risk of malnutrition, bone loss |
| 18.5 – 24.9 | ✅ Normal weight | Lowest risk — ideal range |
| 25.0 – 29.9 | Overweight | Increased risk of diabetes, heart disease |
| 30.0 – 34.9 | Obese Class I | High risk |
| 35.0 – 39.9 | Obese Class II | Very high risk |
| 40.0 and above | Obese Class III | Extremely high risk |
How To Use This BMI Calculator
- Select your unit system — Metric (kg and cm) or Imperial (lbs and ft).
- Enter your current body weight accurately. Weigh yourself without clothes for best results.
- Enter your height without shoes.
- Click Calculate BMI. Your BMI value, weight category, ideal weight range, and visual scale appear instantly.
Limitations of BMI
BMI is a valuable initial screening tool but has recognised limitations. It cannot distinguish between muscle mass and body fat — a highly muscular athlete may show a high BMI despite having very low body fat. BMI also does not account for fat distribution: abdominal fat (visceral fat) carries more health risk than fat stored in the hips and thighs, yet BMI treats all weight equally.
Additionally, research shows that people of South Asian, East Asian, and some other ethnic backgrounds face higher health risks at lower BMI values compared to European populations. For individuals from Pakistan, India, and neighbouring countries, some health organisations recommend using lower BMI thresholds (overweight at 23+ rather than 25+) as a more appropriate risk indicator.
Always use BMI as a starting point, not a final verdict. Combine it with other assessments — waist circumference, body fat percentage, blood pressure, blood glucose — and consult a qualified healthcare professional for a complete health evaluation.
Frequently Asked Questions
According to WHO, a BMI between 18.5 and 24.9 is considered healthy for most adults. Values below 18.5 indicate underweight, 25–29.9 indicates overweight, and 30 or above indicates obesity. These thresholds apply to adults aged 20 and over.
The WHO BMI categories (18.5–24.9 for normal weight) apply equally to men and women. However, women naturally carry a higher percentage of body fat than men at the same BMI. Some researchers suggest that for women, the lower end of the normal range (18.5–22) may be optimal, but this is not an official WHO recommendation.
Yes. A BMI of 27 falls in the overweight category (25.0–29.9). This does not automatically mean poor health, but it does indicate a moderately elevated risk for conditions like type 2 diabetes and cardiovascular disease over the long term. Lifestyle changes such as improved diet and increased physical activity can help bring BMI into the normal range.
Online BMI calculators use the same WHO-standard formula as medical professionals. The mathematical calculation is 100% accurate — the accuracy of your result depends entirely on entering correct weight and height values. The limitation of BMI lies in what it measures, not in how the calculation is performed.
The standard WHO threshold of BMI ≥ 30 for obesity applies in Pakistan under national health guidelines. However, some health experts recommend using a South Asian-specific threshold of BMI ≥ 27.5 to define overweight and ≥ 32.5 for obesity, due to higher visceral fat accumulation in South Asian populations at lower BMI values.