This is a fixed forumula, where BMI = weight (kg) / heigh squared (m2). You'd need to use a calculator to convert imperial measurements to metric, which could be built into the tool.

Source: Hill, A, Marchese, R, 2011. The essential guide to fitness: for the fitness instructor. 2nd ed. page 103: Pearson Australia.

The actual problem here is grading people into a health risk, as the categories change from country to country. I would hate to see DDG just spitting out US-centric results, so you'd need 3 inputs:

1. Height
2. Weight
3. Nationality

My opinion- BMI is inherently flawed and should only be relied upon by general populations as a guide. Other measurements, such as waist to hip ratio (Van Itallie, 1988), would be a better measurement as the research is 16 years ahead and a better indicator of health risk.
posted by glennmatthew 3 years and 5 months ago Link

I agree that BMI is not the best metric for grading weight, that's why I wanted to include a link to the Wikipedia.

As for the grading, it's less dependent on the nationality and more on the age and gender of a person, which is why I'd consider leaving it out for now. Just return the value with a link to a place where you can see where you stand in regards to your age and gender?
posted by rixx 3 years and 5 months ago Link
Wikipedia is probably the safest landing page, since the content can be readily updated as needed.

How would you intuitively capture the inputs? Just a simple "bmi 180cm 90kg" or "bmi 6'1" 200lbs"?
posted by glennmatthew 3 years and 5 months ago Link
Both of these (plus weight in stone) are what I'd be looking for.
posted by rixx 3 years and 4 months ago Link