Metric formula
BMI = weight in kg / height in meters^2
If height is entered in centimeters, convert it to meters first. For example, 175 cm becomes 1.75 m.
Imperial formula
BMI = 703 x weight in lb / height in inches^2
The factor 703 adjusts pounds and inches to match the metric BMI scale.
Worked example
For a person weighing 70 kg and measuring 1.75 m: BMI = 70 / 1.75^2 = 70 / 3.0625 = 22.86. Rounded to one decimal place, the result is 22.9.
How to interpret the result
BMI places weight relative to height on a common adult screening scale. It can be useful for population-level comparison, but it does not show body fat percentage, muscle mass, fat distribution or individual health.
Common mistakes
- Using height in centimeters directly in the metric formula instead of meters.
- Forgetting to square height before dividing.
- Treating the BMI number as a diagnosis rather than a screening index.
- Applying adult BMI categories to children without age- and sex-specific growth charts.
When the formula is not enough
- Children, pregnancy, older adults and highly muscular people may need different interpretation.
- Clinical context, body composition and waist measurement can change what the number means.
- Medical decisions do not belong on BMI alone.
References
- CDC: Adult BMI categories - adult screening category context, accessed 2026-05-17.
- WHO: Body mass index topic page - international BMI context, accessed 2026-05-17.