Common BMI misunderstandings: formula, scope and limits
The short answer
Body mass index (BMI) is weight in kilograms divided by height in metres squared. It is one screening measure, not a diagnosis or a direct measurement of body fat. The standard adult BMI formula is the same for women and men. The same BMI does not establish the same body composition or personal health risk.
Body mass index (BMI) is weight in kilograms divided by height in metres squared. It is one screening measure, not a diagnosis or a direct measurement of body fat. The standard adult BMI formula is the same for women and men. The same BMI does not establish the same body composition or personal health risk.
Units are converted before calculation. Categories use the unrounded result; only the display is rounded. The shortcut multiplier 703 can differ slightly from exact conversion.
For adults aged 20 and older, the standard BMI calculation does not add an age correction. Reference categories alone do not establish an ideal BMI for a particular age. Older adults may need additional clinical context, including muscle and health history; this tool does not supply that assessment. Children and teenagers require a separate age-specific method.
How we calculate
Body mass index (BMI) is weight in kilograms divided by height in metres squared. It is one screening measure, not a diagnosis or a direct measurement of body fat.
Imperial inputs are converted using 1 lb = 0.45359237 kg and 1 in = 2.54 cm. Five feet nine inches is 69 inches, not 5.9 feet.
Units are converted before calculation. Categories use the unrounded result; only the display is rounded. The shortcut multiplier 703 can differ slightly from exact conversion.
Screening scope
Adult (20+), not pregnant. For ages 2–19, use a validated BMI-for-age calculator. This tool shows adult ranges only.
BMI is one screening measure, not a diagnosis or a weight goal. It does not distinguish muscle from fat and is not suitable for pregnancy.
This explanation checks the method and arithmetic. It does not claim an independent medical review. Personal interpretation requires context and an appropriate healthcare professional.
Sources
Sources below are in English.