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At 70 kg and 1.62 m tall, your BMI is 26.7. You get it by squaring the height, 1.62 × 1.62 = 2.6244, and dividing the weight by that: 70 ÷ 2.6244. BMI stands for body mass index, it is written in kg/m², and men and women use the same formula. Where Indian reports differ is the chart the answer is read against.
On the Indian chart, below 18.5 is underweight and 18.5–22.9 is normal. A BMI of 23–24.9 is overweight and 25 or more counts as obesity. The global WHO chart puts those two lines at 25 and 30, so 26.7 is obesity on one report and overweight on another.
BMI is your weight in kilograms divided by your height in metres squared
BMI = weight (kg) ÷ height (m)². You need your weight in kilograms, your height in metres and a phone calculator. Square the height first by multiplying it by itself, then divide the weight by that figure. Divide by the height and square the answer instead, and you get a number far too large.
Take a woman of 64 kg who is 158 cm tall. Her height in metres is 1.58, and 1.58 × 1.58 is 2.4964. Then 64 ÷ 2.4964 gives a BMI of 25.6. With height in centimetres, divide the weight by the centimetres squared and multiply by 10,000: 64 ÷ 24,964 × 10,000 gives the same 25.6.
Feet and inches need turning into centimetres first. A foot is 30.48 cm and an inch is 2.54 cm, so 5 ft 4 in comes to 152.4 plus 10.16, or 162.56 cm. Watch how the height was written down: 5.4 feet on a form means 5 ft 4.8 in, which is not the same as 5 ft 4 in.
Bathroom scales often show pounds too. Multiply the weight in pounds by 703 and divide by your height in inches squared. At 154 pounds and 64 inches that is 703 × 154 ÷ 4,096, or 26.4, and the metric version, 69.9 kg at 1.6256 m, also gives 26.4. Because 703 is rounded, the two can differ in the second decimal, and if you sit right on a line the metric answer is the one to use.
For a spreadsheet, put the weight in kilograms in A2 and the height in centimetres in B2, then type =A2/(B2/100)^2 in C2. It needs nothing but a scale and a tape, which is why the same number appears on almost every health check report, printed beside your height and weight.
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What does BMI stand for, and who came up with it?
BMI stands for body mass index. Lab and hospital reports print it in kg/m², which is the formula written as a unit: kilograms on top, metres squared underneath. A report showing 26.7 kg/m² is giving you the BMI, and nothing needs converting.
The ratio is older than its name. In the 1830s the Belgian mathematician and astronomer Quetelet measured thousands of adults and saw that weight rose roughly with the square of height, not with height itself. For more than a century it was called the Quetelet index and was used to describe whole populations rather than to judge one patient.
The name body mass index dates from 1972 and the American physiologist Keys. His team tested several weight-for-height formulas on men from different countries, measured their body fat, and found this ratio tracked it best. He chose it for studying groups. Doctors later borrowed it for single patients, and most of its limits come from that borrowing.
Which BMI chart applies to Indian adults?
Many Indian doctors and labs use the cut-offs from a 2009 national consensus (Misra): below 18.5 underweight, 18.5–22.9 normal, 23–24.9 overweight, and 25 or above obesity. The same consensus set waist limits of 90 cm for men and 80 cm for women. The global WHO chart sits higher, with normal ending at 24.9, overweight running up to 29.9 and obesity starting at 30, split into classes at 35 and 40.
A WHO expert group reviewed the Asian data in 2004. It kept the global chart for comparing countries and suggested extra action points at 23, 27.5, 32.5 and 37.5 for Asian populations. Depending on the lab, your report may print any of the three, which is why two reports can label the same number differently.
The lower Indian lines come from where the risk shows up. A Canadian study (Razak) found that, for the same trouble with blood sugar and blood fats, the obesity cut-off in South Asian and other non-European groups was about six units below 30. A study of about 1.5 million adults in England (Caleyachetty) found that the diabetes risk a White adult carried at a BMI of 30 was reached by South Asian adults at 23.9.
In India the ICMR-INDIAB survey (Anjana) tested adults across all states. On the Asia-Pacific cut-offs, 28.6% had generalised obesity and 39.5% had abdominal obesity measured at the waist. The waist picked up more adults with extra fat than BMI did, which is why the consensus pairs the two.
Check it yourself in 2 minutes: your BMI, your weight range and your waist
You need a scale, a tape measure and the calculator on your phone. Work out your BMI with the formula above, then run it backwards to see what weight each line of the Indian chart means for your height: weight = BMI × height (m)².
For the woman at 158 cm, her height squared is 2.4964. Multiplied by 18.5 that gives 46.2 kg, the bottom of the normal range. Multiplied by 22.9 it gives about 57 kg, the top of the Indian normal range and seven kilograms below where she stands. Multiplied by 25 it gives 62.4 kg, the start of the obesity band.
Seven kilograms need not be the first target. The 2013 American obesity guideline (Jensen) found that a sustained loss of three to five percent of body weight already improves blood sugar and blood fats, with bigger losses bringing bigger gains. For her, five percent is a little over three kilos, a far easier number to plan around.
Then put the tape round your waist, midway between the lowest rib and the top of the hip bone, breathing out normally. Compare it with the consensus limits of 90 cm for men and 80 cm for women. A waist over the limit with a BMI that looks fine is the pattern the number alone misses, so write both down with the date.
The formula is the same for every adult, though the body behind it is not
A 25-year-old and a 70-year-old, man or woman, all divide weight in kilograms by height in metres squared. What differs is how much fat sits behind the answer. At the same BMI, women carry more body fat than men on average, and older adults carry more fat and less muscle than younger ones. A grandmother and her grandson at a BMI of 24 are not in the same shape.
Ethnic background moves it as well. A meta-analysis (Deurenberg) found that, for the same body fat, Chinese, Thai and Indonesian adults had a BMI about 1.9–3.2 units lower than white adults. Children use the same formula too, but a paediatrician reads the answer on the WHO BMI-for-age curves published in 2007, and the adult cut-offs only take over at nineteen.
What can BMI not tell you about your health?
Take two men at 70 kg and 1.62 m. One played kabaddi through college and still lifts; the other spends ten hours a day at a desk and carries his weight at the belt. Both get a BMI of 26.7, because the formula knows only weight and height.
How often that misleads was measured in a pooled review of 25 studies that tested body fat directly (Okorodudu). The usual cut-offs caught only about half of the adults whose body fat was high. A normal BMI, in other words, is weaker reassurance than a high one is a warning.
The 2025 Lancet commission on clinical obesity (Rubino) wrote this into its definition. Doctors are asked to confirm excess fat with a waist measure or a body fat test, and to check how the organs are coping, before diagnosing obesity from BMI.
The blind spot returns during weight loss, when a crash diet can bring the BMI down by taking muscle with the fat. A doctor-led plan that starts with a home blood test can aim for losing up to 20% of body weight while keeping muscle. It watches the waist and the blood work as well as the scale.