A normal result is a screen, not a clean bill
A BMI of 22 looks tidy on a clinic form.
The figure is one ratio. Kilograms divided by height in metres, squared. Waist size stays invisible. Muscle stays invisible. So does a fasting glucose result.
The color bar uses WHO adult cutoffs for ages 20 or older. Under 18.5. From 18.5 to 24.9. From 25 to 29.9. From 30 upward. Those lines come from population studies of disease risk, mostly in adults of European or North American ancestry.
Drop the same cutoffs onto a 16-year-old, a pregnant patient, or a lifter who squats double body weight. The label starts to mislead.
So why keep the chart? Clinics, insurers, plus research papers still sort people with this ratio. Bring a better measurement when you have one. Use the gauge when a form asks for the index.
The arc is linear from 15 to 40, so the rose section is the longest. A result of 27 sits near the top of the dial, not in the middle of the amber slice. Middle of the dial is 27.5.
One height, four labels
Fix the height at 175 cm, about 5 ft 9 in. Only the kilograms move.
| Weight | BMI | General WHO band |
|---|---|---|
| 52 kg | 17.0 | Underweight |
| 70 kg | 22.9 | Normal |
| 88 kg | 28.7 | Overweight |
| 112 kg | 36.6 | Obese, class II |
70 kg and 88 kg sit 18 kg apart. Different bands. The boundary at 25 is a population cutoff, not a switch inside a body. Nothing biological flips between 24.9 and 25.0.
Healthy kilograms at 175 cm run from 56.7 to 76.3, the weights that land on 18.5 through 24.9. On a pound scale that window is about 125 to 168 lb.
Want a single target instead of a window? The ideal weight calculator runs four clinical formulas from height, with sex and frame size in the mix. Those formulas disagree with each other, which is useful. A range of answers is harder to treat as a command.
Seoul uses a tighter line than London
In 2004 a WHO expert consultation looked at Asian populations and added public-health action points at 23 and 27.5. Diabetes and cardiovascular disease were showing up at lower indexes than the general chart expects.
Singapore's Health Promotion Board still marks 23.0 to 27.4 as moderate risk and 27.5 upward as high risk. Japan treats 25 as obese, which is only the overweight line on the general WHO chart.
General WHO, ages 20 or older
- Under 18.5
- Underweight
- 18.5 to 24.9
- Normal
- 25.0 to 29.9
- Overweight
- 30.0 to 34.9
- Obese, class I
- 35.0 to 39.9
- Obese, class II
- 40 or above
- Obese, class III
Action points used for many Asian adults
- Under 18.5
- Underweight, same floor
- 18.5 to 22.9
- Lower risk on the Singapore chart
- 23.0 to 27.4
- Increased or moderate risk
- 27.5 or above
- High risk
- Japan
- Obesity starts at 25
The gauge on this page stays with the general WHO bands. A clinic in Singapore wants the tighter set. Read the number, then apply the labels your clinic uses. The division is identical either way.
Painting every visitor with the Asian points would mislabel readers whose clinics use the general chart. The reverse mistake is equally common. Country detection will not fix that. You know which form you are filling in.
Sitting at 30 or above? Stop rerunning the same two inputs. Waist circumference tells you where the weight sits. A tape-based estimate tells you whether the kilograms are fat, muscle, or both. Daily intake is a separate question.
The body fat calculator uses the US Navy tape method. The calorie calculator estimates intake from age, sex, plus activity. Resting burn, before activity, sits on the Harris-Benedict BMR calculator.
Kilograms over metres squared
The adult formula is weight in kilograms divided by height in metres squared.
172 cm becomes 1.72 m. Square the height: 2.9584. Divide 81 kg by 2.9584. Result: 27.4. Overweight on the general chart. Slightly under the Asian high-risk point at 27.5. Do not treat 27.4 as a different kind of result from 27.6. Boundaries are where this chart is weakest.
Imperial form, for a scale that speaks pounds: weight in pounds multiplied by 703, then divided by height in inches squared. At 5 ft 10 in (70 inches) with a weight of 180 lb: 180 times 703 equals 126,540. Divided by 4,900 equals 25.8.
BMI prime divides the result by 25. At 27.4 the prime is 1.10, ten percent above the line where the general chart switches to overweight. A prime under 1.00 is still inside the normal band or below it. The tile on the gauge shows that distance from 25 without a second division.
Quetelet proposed the ratio in the 1830s as a way to describe populations, not to grade a single patient. Height squared was a compromise fit. Adults at the tall end score a little high for their build. Adults at the short end score a little low. The ponderal index cubes the height and behaves more evenly at those extremes. Clinics, insurers, plus research papers still ask for the squared version, so this page refuses to swap in a different formula. If the form says BMI, squared height is the number they want, even where the fit is clumsy.
Throw the adult chart out in these cases
Under 20
Growing bodies need BMI-for-age percentiles from CDC or WHO growth charts. An 18.0 in a 14-year-old often falls inside a typical percentile for that age. The same 18.0 in a 40-year-old is under the adult floor. This calculator has no percentile tables.
Wrong tool for a teenager.
Pregnancy
Clinics record BMI from pre-pregnancy weight. The current scale includes the fetus, the placenta, plus extra fluid. A third-trimester reading will look obese on a person who entered pregnancy at 23. Use the earlier weight, or skip the index until after delivery.
A lot of muscle
A front-row rugby player at BMI 31 with low fat mass is the classic failure. The index cannot see a squat rack. When the mirror and the number disagree, move to the body fat calculator. Tape methods still miss visceral fat, and they drift a few points away from a DEXA scan. They do see composition, which this ratio never will.
After 65
Several large cohort studies place the lowest mortality slightly above BMI 25 in older adults. A lower weight sometimes tracks illness and lost muscle rather than a trim diet. The 18.5 floor is the wrong target when weight is falling without a reason. Talk with a clinician about that drop. Chasing a higher number on purpose misreads those studies.
Heights and bodies the ratio mishandles
Under about 140 cm, over about 200 cm, edema, amputations, contest-condition bodybuilding. The ratio gets noisy. Say so before you screenshot the gauge. The page also refuses inputs under 100 cm or 25 kg, because the adult chart was not built for them.
One limit is easy to miss. Shared links store height and weight in the URL. The math never leaves your browser. Toolexe does not save the numbers. Copy a link into a chat and you have published your weight. Skip the share row if that bothers you.
Steps and sleep sit next door if the number sent you looking for habits rather than another index. The steps to calories calculator turns a step count into a rough burn. The sleep calculator works from sleep cycles, which this chart does not touch.
