How this calculator works
- Step 1Weight68.0 kgBody weight in kilograms.
- Step 2Height squared1.7 m × 1.7 mHeight in metres, multiplied by itself.
- Step 3BMI23.5Weight ÷ height², then placed in a band.
Body mass index (BMI) is weight in kilograms divided by height in metres squared. The calculator rounds it to one decimal, as the published tables do, and then shows where it falls on three scales.
The scales are the WHO adult categories, the WHO action points for Asian populations, and the 2009 Indian consensus cut-offs for Asian Indians. All three are for adults aged 18 and over.
Worked example
- BMI
weight (kg) ÷ height (m)²- Band
BMI to one decimal, matched to each table
- kgWeight 68.0 kg
- mHeight 1.7 m
- Height squared1.7 × 1.72.89 m²
- BMI to one decimal68.0 kg ÷ height²23.5
- WHO adult categoryNormal weight
- WHO Asian action pointsAt or above 23.0
- Indian consensus (Asian Indians)Overweight
The same person sits in the WHO normal range but above the Indian consensus normal range. At 170.0 cm, BMI 18.5 to 24.9 is 53.5 to 72.0 kg, while 18.0 to 22.9 is 52.0 to 66.2 kg.
In imperial units, 5 ft 9 in and 160 lb give a BMI of 23.6. Switching units changes only how you type the figures; the stored height and weight are not rounded.
Three scales, side by side
- WHO adult categories18.5 to 24.9Below 18.5: Underweight. 18.5 to 24.9: Normal weight. 25.0 to 29.9: Pre-obesity (overweight). 30.0 to 34.9: Obesity class I. 35.0 to 39.9: Obesity class II. 40.0 or more: Obesity class III
- WHO action points, Asian populations23.0 · 27.5 · 32.5 · 37.5Points at which countries may act on rising risk. No single cut-off fits all Asian groups.
- Indian consensus, Asian Indians18.0 to 22.9Below 18.0: Below the normal range. 18.0 to 22.9: Normal. 23.0 to 24.9: Overweight. 25.0 or more: Obesity
A 2004 WHO expert consultation found that many Asian people face higher risks of type 2 diabetes and heart disease at a BMI below 25. It kept the WHO categories as the international standard and added public-health action points along the scale.
In 2009, an Indian expert consensus published in the Journal of the Association of Physicians of India set lower limits for Asian Indians: normal 18.0 to 22.9, overweight 23.0 to 24.9, obesity 25.0 or more.
Band edges and rounding
BMI is placed in a band after rounding to one decimal, because the tables are written that way.
The WHO table lists normal weight as 18.5 to 24.9 and the next band from 25.0. So a BMI of 24.96 has no band unless it is rounded first. Rounded to one decimal it reads 25.0.
For example, 160.0 cm and 63.9 kg give a BMI of 25.0, which is “Pre-obesity (overweight)” on the WHO scale. Small changes near a band edge mean little; the bands are not sharp health lines.
What BMI leaves out
- Muscle versus fatMuscular people can have a high BMI without excess fat.
- Where fat sitsWaist size adds information that BMI does not capture.
- Children and teenagersUnder 18, BMI is read on BMI-for-age charts instead.
- Pregnancy and illnessAdult bands are not meant for pregnancy or some medical conditions.
BMI is a quick screening number for groups and for a first look. It is not a diagnosis. A health professional considers it alongside other measurements and your history.
For anyone under 18, this calculator does not give a result. The WHO uses BMI-for-age growth references for children and adolescents, which compare a child with others of the same age and sex.
Beyond BMI
BMI compares weight with height only. Body fat, energy needs and ideal weight answer other questions.
To estimate body fat from tape measurements, use the body fat calculator. The ideal weight calculator compares four published formulas, and the BMR and TDEE calculator estimates daily energy.
Common mistakes
Mistake: Read the WHO category alone if you are of South Asian origin.
Instead: Look at the Asian action points and the Indian consensus band as well.
Mistake: Use adult bands for a child or teenager.
Instead: Use BMI-for-age charts with a paediatrician or health worker.
Mistake: Measure height in shoes or weight in heavy clothing.
Instead: Measure barefoot, in light clothing, at a similar time of day.
Mistake: Treat one BMI number as a diagnosis.
Instead: Discuss it with a health professional alongside other checks.
Checking the method
The calculator reproduces WHO/Europe’s own worked example and independent golden values.
WHO/Europe’s published example, 70.0 kg at 175.0 cm, gives a BMI of 22.9. A separate Python script recomputes every test case with exact fractions, classifies with its own copy of the cut-offs, and solves the weight ranges numerically.
Pounds and inches use the exact definitions: 1 lb is 0.45359237 kg and 1 inch is 2.54 cm. The sources below were opened and checked on the review date.
Read how we test our calculators, or browse more health calculators.