What is BMI and how is it calculated
Body Mass Index (BMI) is a numerical value calculated from your height and weight. It is a widely used screening tool to categorise whether a person is underweight, normal weight, overweight, or obese. The formula is: BMI = weight in kilograms divided by (height in metres squared). For example, a person weighing 70 kg who is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.
BMI categories
The WHO defines the following BMI categories: below 18.5 is underweight, 18.5 to 24.9 is normal weight, 25.0 to 29.9 is overweight, 30.0 to 34.9 is obese class I, 35.0 to 39.9 is obese class II, and 40.0 and above is obese class III (morbidly obese). Some Asian health organisations use lower thresholds because South and East Asian populations show increased health risks at lower BMI values — overweight may be defined as BMI above 23 rather than 25.
BMI limitations
BMI is a screening tool, not a diagnostic measure. It does not distinguish between muscle mass and fat mass — a muscular athlete may have a high BMI but low body fat. It does not account for the distribution of body fat (visceral fat around the abdomen carries more health risk than subcutaneous fat). Elderly individuals may have normal BMI but carry excess body fat due to muscle loss. Pregnant women require different assessment. Despite these limitations, BMI remains the most widely used initial screening tool due to its simplicity.
Healthy weight for Pakistanis and South Asians
South Asians including Pakistanis and Indians tend to accumulate more visceral (abdominal) fat at lower BMI levels compared to Western populations. Pakistani medical associations generally recommend a BMI target of 18.5 to 22.9 as optimal, and flag overweight risk from BMI 23 onwards. Waist circumference is also an important measure — above 90 cm for men and 80 cm for women indicates elevated cardiometabolic risk for South Asians.
Frequently Asked Questions
What is a healthy BMI for adults? The standard healthy range is 18.5 to 24.9. For South Asian adults, some clinical guidelines recommend a lower upper limit of 22.9 as optimal.
Is BMI accurate for children? BMI for children and teenagers is age and sex-specific (called BMI-for-age percentile) and not interpreted using the same categories as adults. Use a paediatric growth chart for children.