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26.5
Overweight on the WHO scale
An estimate for screening, not a diagnosis and not medical advice. BMI is weight against height and nothing else: it cannot tell muscle from fat, so it reads high for a heavily built athlete and low for someone with little muscle at a normal weight. It says nothing about where fat is carried, which is the part that tracks health risk most closely.
The WHO cut-offs above are the international ones. The same WHO expert consultation (Lancet, 2004) added 23 and 27.5 as public-health action points for Asian populations, where diabetes and cardiovascular risk climb at a lower BMI — shown above as a second reading of the same number. Adult figures only: children and teenagers are assessed against age-and-sex percentiles, and BMI is not interpretable during pregnancy.
Body mass index is your mass in kilograms divided by the square of your height in metres. Adolphe Quetelet worked it out in the 1830s while describing the average build of a population, and that is still what it does best: a fast, cheap screening statistic for large groups rather than an assessment of one person. This calculator returns the index, the World Health Organization band it falls in, and — more usefully than either — the weight band that would put your own height inside the healthy range.
Someone 178 cm tall weighing 84 kg has a BMI of 26.5, which the WHO calls overweight. The healthy band for that height runs from 58.6 kg to 78.9 kg, so they sit 5.1 kg above the top of it — a far more actionable sentence than the index itself.
The same person in imperial units is 5 ft 10 in and 185 lb, and the index is again 26.5, with the band reading 129 lb to 174 lb. Notice how wide that is: 45 lb separates the bottom of healthy from the top at one height, which is the first clue the index is not precise enough to argue over half a point of.
The index knows your mass and your height and nothing else. It cannot tell muscle from fat, so a heavily built rower and a sedentary person of the same weight get the same reading, and the rower is routinely classified as overweight. It runs the other way too: someone can sit comfortably in the healthy band with very little muscle and a great deal of abdominal fat.
It says nothing about where fat sits either, which is the part that tracks metabolic risk most closely — a waist measurement carries information the index structurally cannot. And it is calibrated on adults: children are assessed against age-and-sex percentile charts, and it is not interpretable at all during pregnancy.
The bands come from the WHO technical report on obesity published in 2000: under 18.5, healthy to 25, overweight to 30, then three classes of obesity at 30, 35 and 40. They are round numbers chosen for surveillance, and nothing changes about a body as it crosses one.
A later WHO expert consultation, published in the Lancet in 2004, kept those international cut-offs and added 23.0 and 27.5 as further action points, because risk of type 2 diabetes and cardiovascular disease starts climbing at a lower index across much of Asia. Both readings of the same number are shown rather than one chosen for you.
Close to it, for you personally. Muscle is denser than fat, so a well-trained body reads high and can land in the overweight or obese band at a genuinely low body fat percentage. Use a tape measure or a body composition estimate instead, and treat the index as a number for statisticians.
Because pounds per square inch and kilograms per square metre are different units, and converting between them means multiplying by roughly 703.07 — rounded to 703 for hand arithmetic. It is a unit conversion hiding in a constant, not a separate formula, and the rounding shows up in the third decimal place.
They exist because population studies found metabolic risk rising earlier in South and East Asian groups at the same index. The WHO presented them as additional action points rather than a replacement classification, so they are a reason to look more closely rather than a different verdict. Someone who knows your history should make that call.
No. Blood pressure, blood lipids, fitness, sleep, smoking and family history all predict outcomes better, and plenty of people inside the healthy band have poor readings on every one of them. A number in range is one reassuring data point among many, not a clean bill of health.