How is BMI calculated?

BMI is weight in kilograms divided by height in metres squared. In imperial units the equivalent formula is 703 times weight in pounds divided by height in inches squared. The result is the same number in kg per metre squared either way.

What are the WHO BMI categories?

The World Health Organization bands are: below 18.5 underweight, 18.5 to 24.9 normal weight, 25 to 29.9 overweight, 30 to 34.9 obese class I, 35 to 39.9 obese class II, and 40 or above obese class III. This tool labels your result against these cut-offs.

Is BMI accurate for everyone?

No. BMI does not distinguish muscle from fat, so very muscular people can read as overweight while having little body fat. It also ignores fat distribution and is less reliable in older adults, athletes, and during pregnancy. Treat it as a screening number, not a diagnosis.

What is a healthy weight for my height?

The tool shows the weight range that corresponds to a BMI between 18.5 and 24.9 at your entered height. Staying within that range is the conventional definition of a healthy weight, though waist measurement and body composition add useful context.

Does BMI differ by ethnicity?

Some health bodies use lower overweight and obesity thresholds for South Asian and certain other populations because cardiometabolic risk rises at a lower BMI. This calculator uses the standard WHO international bands, so interpret borderline results with that in mind.

Adult BMI Calculator & WHO Classification

Body Mass Index is the most widely used screening measure of whether a person’s weight is in a healthy range for their height. It is quick, needs only two numbers, and gives a single value that maps onto the World Health Organization’s weight categories.

How it works

BMI divides body mass by the square of height, which removes most of the effect of being tall or short and leaves a number that tracks body fatness across the population.

metric:   BMI = weight(kg) / height(m)^2
imperial: BMI = 703 x weight(lb) / height(in)^2

The calculator also works backwards from your height to show the weight range that keeps BMI between 18.5 and 24.9, the WHO normal band.

Categories, example, and notes

A worked example: a person 1.75 m tall weighing 72 kg has a BMI of 72 / (1.75 x 1.75) which is about 23.5, placing them in the normal band. The full set of WHO cut-offs runs from underweight below 18.5 up to obese class III at 40 and above. Remember that BMI cannot tell muscle from fat and ignores where fat is stored, so a muscular athlete may register as overweight while carrying little fat. For a fuller picture, combine BMI with waist circumference and, where relevant, a lean body weight estimate.