How it works
BMI is weight divided by height squared. It is a screening ratio, not a body-fat measurement and not a diagnosis. This page reports it to one decimal place and then labels that rounded number three ways: the WHO international cut-offs, the Chinese adult standard WS/T 428-2013, and the public-health action points from the WHO expert consultation published in The Lancet in 2004. A person can be “normal” on one row and “overweight” on another. That disagreement is the reason the three rows are separate.
In metric units, BMI = kilograms ÷ (centimeters ÷ 100)². In imperial units the page first converts with the international pound, 0.45359237 kg, and the inch, 2.54 cm, and then uses the same formula. It does not multiply by the rounded factor 703. Results are rounded to one decimal with ordinary half-up rounding, and the labels use that rounded value. 65 kg at 170 cm is 65 ÷ 1.7² = 22.4913, which rounds to 22.5.
What each row is allowed to say
The WHO row follows the adult cut-offs in Technical Report Series 894: under 18.5 underweight, 18.5 to 24.9 normal, 25.0 to 29.9 overweight, 30.0 and above obesity. On this page the test is the one-decimal number: 24.9 is still normal, 25.0 is overweight, 29.9 is overweight, 30.0 is obesity.
The China row follows WS/T 428-2013, Criteria of weight for adults, which China CDC has circulated as the adult weight standard. Under 18.5 is underweight, 18.5 up to but not including 24.0 is normal, 24.0 up to but not including 28.0 is overweight, and 28.0 and above is obesity. The 2004 Lancet consultation did not adopt 24 and 28 as the Asian rule. Those two numbers are the Chinese standard, and the page labels them that way.
The Asia row is the 2004 consultation’s action points, not a replacement WHO classification. The consultation kept the international cut-offs and added points along the scale: 23.0, 27.5, 32.5, and 37.5 kg/m². Below 18.5 stays underweight. From 18.5 up to but not including 23.0 the page says “below the 23 action point”. From 23.0 up to but not including 27.5 it says increased risk. From 27.5 up to but not including 32.5 it says high risk. From 32.5 upward it says very high risk. The consultation did not declare a single obesity cut-off for every Asian population.
The same body, three labels
At 170 cm and 65 kg the rounded BMI is 22.5. WHO says normal, China says normal, and the Asia row is still below 23. At 170 cm and 70 kg the value is 70 ÷ 2.89 = 24.221, which rounds to 24.2. WHO still says normal. China says overweight, because 24.2 is at or above 24 and below 28. The Asia row says increased risk, because 24.2 is at or above 23 and below 27.5. At 170 cm and 80 kg the value is 27.7: WHO overweight, China still overweight (obesity starts at 28.0), Asia high risk. At 170 cm and 81 kg the value is 28.0: China moves to obesity while WHO is still in the overweight band.
Seventy inches and 160 pounds become 177.8 cm and 72.5748 kg. The BMI is 22.957, which rounds to 23.0. WHO and China both say normal. The Asia row says increased risk, because 23.0 is not below the action point. If you type 70 and 160 while the metric fields are selected, the page treats them as centimeters and kilograms and the result is nonsense. Switch the unit before you read the label.
Notice
This is not a diagnosis, a treatment plan, or a measure of body fat. Athletes, pregnant people, children, and older adults with low muscle mass are outside the populations these adult cut-offs were written for. Do not change diet or medication from this number. Take questions to a clinician who can see you.
Worked examples
Input: 170 cm, 65 kg
Output: 22.5. WHO normal, China normal, Asia below the 23 action point
Input: 170 cm, 70 kg
Output: 24.2. WHO normal, China overweight, Asia increased risk
Input: 70 in, 160 lb
Output: 23.0. WHO normal, China normal, Asia increased risk
Limits
- Labels follow the rounded one-decimal BMI. 23.96 displays as 24.0 and is overweight on the China row.
- The cut-offs are for adults. WS/T 428-2013 says the standard is not for athletes or for pregnant women. Children need a growth reference, not these bands.
- Muscle, edema, and height measured in shoes all move the number without describing fat mass.
Common mistakes
- Reading only the WHO row and telling someone at BMI 24.2 that every standard calls them normal.
- Quoting “WHO Asia uses 24 and 28”. The 24/28 pair is WS/T 428-2013. The 2004 WHO consultation named 23 and 27.5 as action points and kept 25 and 30 as the international classes.
- Leaving inches in the centimeter box after toggling the unit.
Questions
Why is 22.5 the default?▾
Does a high BMI mean I have obesity disease?▾
What about waist circumference?▾
Sources
- WHO. Obesity: preventing and managing the global epidemic. WHO Technical Report Series 894. Geneva: World Health Organization; 2000. Adult cut-offs 18.5, 25, and 30.
- WHO expert consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet. 2004;363(9403):157-163. Action points 23.0, 27.5, 32.5, and 37.5, with the international cut-offs retained.
- WS/T 428-2013. Criteria of weight for adults. Adult BMI bands: <18.5, 18.5 to <24.0, 24.0 to <28.0, ≥28.0. China CDC has published the standard’s scope, including the note that it is not for athletes or pregnant women.