Fried:
How many pounds do I have to gain to move up a Jean size? Iām currently a 31 at 160lbs and 5ā10, looking to eventually fill out a 33.
This question doesn't seem to have a clear answer.
It may be possible to guessimate with linear regression or multiple regression, but that requires a lot of information that so far as I know, doesn't really exist since the sample size is far too small.
In particular, I would need a lot of gainers (male and female) to very regularly measure various measurements over time. I'm also not sure how one might account for genetics. For example, some women are just plain more bottom heavy than others.
Your best best might be the various body visualizers you can find online. However, they too are largely inexact. Though when you adjust one measurement on one, they'll usually compensate the other measurements to match the specified weight, which might get it a little closer.
Regardless, one thing that's clear is there isn't a fixed number. It would take more and more weight, with every additional inch.
To really simplify things, if you consider a circle, it takes more and more area for each additional unit of circumference and especially radius. If you consider a cylinder, it takes more and more volume for each additional unit of circumference or diameter.
Perhaps the good news is that at that size, you probably don't need to gain that much more to go from 31 to 33. Getting from 36 to 38 could be potentially more difficult, and 38 to 40 means even more weight and more food.