…like there’s a body-mass index calculator? You’d plug in your height and your weight, and instead of your BMI it calculates your waistband (or dress size, or whatever).
This would be so people could say “OK, to fit that size of pants I need to lose/gain that much weight.” Because you know the weight & BMI are incidental. It’s the clothes size that matter.
Waist sizes vary so much even within the same weight/ht ranges a calculator of this sort would be difficult to make accurate. I’m 6’3" & 235 labs with a relatively narrow waist, and relatively thick “tree trunk” style thighs. Other guys might have a thicker waist & more slender legs & be equally fit. It’s not (IMO) a viable measure.
And dress sizes vary even more, and more randomly. One manufacturer’s size 6 may be another’s size 10.
If you waste size is larger than your chest size you are too fat 