"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"
Waist to height is the only proven metric. And the problem with BMI is not that it is overestimating fat, it's that it's underestimating fat because it completely misses skinny-fat people, and the number of those is much higher than the number of jacked overweight not fat athletes.
Add to this the complicating factor that it's really torso fat that is metabolically active and dangerous to your health.
Waist should be less than half your height, you don't even need a measuring tape. Get someone to cut a string as long as you are tall, and see if it can go around your waist twice, with at least some extra length. If so, you are good, probably don't have too much torso fat.
ETA I don't understand why they need that complicated formula, why not just a ratio? The only inputs are waist and height. Never understood the point of squaring height to get BMI either, it's also just a mass to height comparison, why not a simple ratio?
Right, you are proportionate, waist to height as a measurement means a 7' tall guy would be healthy with a 40" waist, but a lady (or man) who is 5' tall really does need smaller than 30" to be in shape.