How this calculator works
BMI = weight (kg) / height (m)². Imperial inputs convert using 1 lb = 0.45359237 kg and 1 inch = 2.54 cm before calculation.
CDC adult boundaries: below 18.5 underweight; 18.5 to below 25 healthy weight; 25 to below 30 overweight; 30 to below 35 obesity class 1; 35 to below 40 class 2; 40 and above class 3. Categories use the unrounded result, so a value very close to a boundary can round to the boundary itself.
Reading your result
BMI is a screening measure, not a diagnosis or fitness score. It cannot separate muscle, fat and bone, or locate fat distribution. Interpret it alongside clinical context and other measures; a category does not prescribe a target weight.
Illustrative worked example
For an adult aged 30, 175 cm tall and weighing 70 kg: 70 / 1.75² = 22.86 kg/m², in the CDC healthy weight category.
Supported inputs & limitations
CDC adult interpretation begins at age 20. helsi accepts ages 20–100, height 120–230 cm and weight 30–300 kg. Younger people need age- and sex-specific interpretation. Pregnancy, altered body proportions and high muscularity limit the meaning of the result.
Sources & methodology
These primary sources support the method and context. They do not endorse helsi or verify this implementation.