Formula and interpretation
BMI is calculated by dividing weight in kilograms by height in metres squared. Adult BMI categories are commonly interpreted as underweight, healthy weight, overweight and obesity ranges. The result also shows BMI Prime, which compares your BMI with the common adult overweight threshold of 25, and ponderal index, which can be useful when comparing people with very different heights.
Example
For an adult who is 175 cm tall and weighs 70 kg, BMI is 70 / 1.75^2 = 22.9. The same BMI formula can also be calculated from imperial units after converting pounds and inches.
Common mistakes
Do not use adult BMI categories for children, teenagers or pregnancy. Also avoid treating a BMI category as a diagnosis; it does not measure body fat distribution, muscle mass or overall health.
Assumptions and limitations
This calculator is for adults. BMI does not directly measure body fat, muscle mass, fat distribution or individual health. Children, teenagers, pregnancy and some athletes need different interpretation. Some public-health tools also show child/teen percentiles or ethnicity-specific context; this page deliberately keeps the adult calculation separate so the category label is not overextended.
Useful follow-up checks
- If BMI is near a category boundary, small measurement or rounding differences can change the label.
- If body composition is unusual, use BMI as a screening number rather than a personal health conclusion.
- For children and teenagers, use an age- and sex-specific child BMI percentile tool from a public-health source.
References
- World Health Organization: Obesity and overweight, accessed 2026-05-13.
- NHS BMI calculator, accessed 2026-05-13.
- CDC adult BMI categories, accessed 2026-05-13.
FAQ
Is BMI a diagnosis?
No. BMI is a screening estimate and is not enough on its own to diagnose health.
Why can BMI be misleading?
It does not distinguish fat from muscle and does not account for all differences in age, sex, ethnicity or body composition.
Last reviewed: 2026-05-13