BMI calculator (body mass index)

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Enter your weight and height to see your BMI and category under the criteria you choose. BMI is a basic screening measure for adults, not a diagnosis.

What the result means

BMI (body mass index) compares weight with height. It is a first-line screening measure for adults; the same value can mean different body-fat levels in different people.

The WHO international classification uses cut-offs of 18.5 / 25.0 / 30.0. The adult cut-offs used by Thailand's Department of Health (in line with the WHO 2004 public-health action points for Asian populations) use 18.5 / 23.0 / 25.0 / 30.0. This tool shows the two classifications separately and never mixes them.

The "normal" weight range is worked back from your height under the chosen classification. It is a reference range, not a target you must reach.

How it is calculated

BMI = weight (kg) ÷ height (m)²
The category is assigned from the exact value before rounding; the displayed value is rounded to one decimal place. So an exact 24.96 shows as 25.0 but is still "normal" under WHO because the exact value is below 25.0
If you enter pounds/inches, they are converted first: 1 lb = 0.4535924 kg · 1 in = 2.54 cm (NIST SP 811)
"Normal" weight range = lower cut-off × height (m)² to upper cut-off × height (m)²

Limitations and cautions

BMI cannot distinguish fat, muscle and bone (CDC); muscular people may have a high BMI without high body fat
The same BMI can reflect different body-fat levels in different populations (WHO), which is why separate Asian cut-offs exist
Not for children and teenagers under 18, or during pregnancy
Older adults, athletes and people with medical conditions should interpret results with a health professional

Results are estimates or basic screening only, not a medical diagnosis or medical advice.

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References

Compiled by Well Nutrition Hub from the sources listed. Content last reviewed 16 Oct 2026.