Q.What is BMI? Calculate BMI of a child whose weight is 72 kg and height 1.68 mt. (Attempt any 5 of Q19-24)

Body Mass Index Calculation

Body Mass Index, or BMI, answers a very practical question: given how much a person weighs, is that weight reasonable for how tall they are? A person weighing 70 kilograms might be perfectly healthy at 1.8 metres tall but clearly overweight at 1.5 metres tall. BMI is the calculation that adjusts weight for height so the two can be compared fairly.

The Formula

BMI is calculated as:

BMI = body weight in kilograms divided by (height in metres, squared)

The result is expressed in kilograms per square metre (kg/m²). Two things to get right when calculating it: weight must be in kilograms, and height must be converted to metres (not centimetres) before it is squared. A common error is squaring the height in centimetres, which produces a meaningless number.

Working Through an Example

Suppose a person weighs 63 kilograms and is 1.5 metres tall. First, square the height: 1.5 multiplied by 1.5 gives 2.25. Then divide the weight by this figure: 63 divided by 2.25 gives 28, so this person's BMI is 28 kg/m². That figure is then read against a classification scale to see which category it falls into — for instance, a value of 30 kg/m² or above is commonly taken as the threshold for obesity.

Why the Calculation Matters, Not Just the Category

It is easy to jump straight to the category (underweight, normal, overweight, obese) and skip the arithmetic, but understanding the calculation itself matters for two reasons. First, it shows why BMI treats a tall, heavy person differently from a short, heavy person — the height term does real work in the formula. Second, it lets a student verify or recompute a BMI value directly from raw height and weight figures, rather than relying on memory of where the category boundaries sit.

A Genuine Limitation …