“The body mass index has long been criticized as a flawed indicator of health. A replacement has been gaining support: the body roundness index.” Article unfortunately doesn’t give the freaking formula for chrissakes; it’s “364.2 − 365.5 × √(1 − [waist circumference in centimeters / 2π]2 / [0.5 × height in centimeters]2), according to the formula developed by Thomas et al.10”
I went from Anorexia in the military to getting out and doing calisthenics for years now. I am quite a bit smaller than average. Usually between 13-17%, primarily using Navy Body Fat measurement scale to determine it.