Estimating Sizes for Weight Gain

One of the things I struggle with is how to conceptualize what weight gain looks like at any given stage. What does an extra 20 lbs look like? What about 50? A few hundred? What size clothing do people wear at a given weight? And how much bigger do you actually have to be to pop a button or start outgrowing furniture?

So I’ve put together this post for a few of the tools I use to estimate size under weight gain.

  1. Don’t. Measure instead.

If you can find real-world measurements of big beautiful and handsome people that match what you’re looking for, why bother estimating? Potential sources include: Fantasy Feeder, OnlyFans, Curvage, non-kink/non-sexual site My Body Gallery and yourself or a willing partner.

  1. Estimating waist size by weight:

There is no definitive lbs-to-waist-inches conversion because all bodies are different. But here are a pair of attempts to estimate:

A. This data analysis of 46 r/progresspics redditors and their weight loss suggests that:
–Losing 55 lbs (25kg) or less means 6.1 lbs lost = 1 inch lost (and 1.1 kg lost = 1 cm lost)
–Greater weight loss means 8.5 lbs lost = 1 inch lost (and 1.5 kg lost = 1 cm lost)

Reversing these gives a crude but simple way to estimate how much a character’s waistline expands with weight

–46 is a very small sample size, especially for self-reported numbers, which makes this less reliable
–Does not account for water weight, muscle weight, or body shape

B. This 2012 paper from BMC Medical Research Methodology has multiple formulas to predict waist size in cm based on age, BMI, sex, and race.

Male: 22.61306 + (2.520738*(BMI)) + (0.1583812*(Age)) − (3.703501*(Black – will be 0 or 1)) − (1.736731*(Hispanic – will be 0 or 1))

Female: 28.81919 + (2.218007*(BMI)) − (3.688953*(OlderThan35 – will be 0 or 1)) + (0.125975*(Age)(OlderThan35 – will be 0 or 1)) − (0.6570163(Black – will be 0 or 1)) + (0.1818819*(Hispanic – will be 0 or 1))

The researchers found that these formulas had a median accuracy of 0.1 cm and, at the most varied , accuracy within 3-4 cm (1-1.5 inches)

–Deliberately excluded people with a BMI > 40 from dataset
–Complicated with little payoff. Spot-checking, it’s fairly close to the 6.1 lbs = 1 inch from method A

  1. Estimating width by waist size:

IRL people are not spheres (sorry blob fans!). The cross-section of a given person’s waist/belly is not going to be a circle, but an ellipse. This sucks, because the formula for calculating the perimeter of an ellipse is complicated. Fortunately, someone made a nice web tool that calculates it for you. I use this to try to figure out how big a character can get before they have to worry about armrests (or doors). I unfortunately don’t have a good way of estimating the axes A and B, so I eyeball it and hope for the best.


  1. Estimating clothing Sizes:

If you already know your character’s dimension, Size Charter can help you find the right size in a given brand. If not, this Lifehacker article from 2019 ranks clothing brands on how small, big, or true-to-life they run.

For very big sizes, here’s a list of stores aimed at women that carry up to 6X or bigger. At a glance, Hey Maven seems to carry the largest sizes out of that list. I couldn’t find a similar list aimed at men, but KingSize goes up to 10XL, and Big Dude Clothing goes up to 8XL.

–Size charts don’t care about body shape. For example, Pear-shaped people will like need a size or more up on bottoms.
–As above, sizes between brands are not consistent. This is especially important to remember when moving between general big-box stores and dedicated plus-size brands

  1. Estimating Size to Pop a Button/Bust a Seam

I wish I had a good way to estimate this. Instead, I think about this quiet-admirer post, where they and several gainers in the comments talk about gaining 30, 45, even 60 lbs and still being able to button jeans and not split seams.

  1. Don’t. Measure with your heart.

It’s porn. Break out the intergalactic charts if you need to. Do what you like. :stuck_out_tongue:


This isn’t possible though 6.1 lbs lost = 1 inch lost because the fatter you are the more weight you gain per inch.

It’s mentioned here Need some help with optimizing a multiple path visual novel without having to make a ton of renders - #7 by dingotush

But also that just makes sense in order to double the volume of a sphere you don’t have to double it’s radius.

But I guess Female: 28.81919 + (2.218007*(BMI)) − (3.688953*(OlderThan35 – will be 0 or 1)) + (0.125975*(Age)(OlderThan35 – will be 0 or 1)) − (0.6570163 (Black – will be 0 or 1)) + (0.1818819*(Hispanic – will be 0 or 1)) would work? Although, I’m not sure how helpful this is. Because bmi is based on height and weight, you can’t use bmi in relation to waist size. Really the most important formula is waist size to weight. At least for daz3d where you can measure metrics the waist size.

Going back to dinotush’s post… I wonder how to calculate the change from weight squared from girth to the 1.41 power.
Okay I think I get it now so if weight is doubled that means weight=weight^2 and sqrt(2) is 1.41 so waist goes up by waist^1.41
So if weight goes from 30inches to 40inches that’s 30^x=40 so uh. Which makes x = 1.0845 and the square of that is… 1.1761 so uh new weight is equal to old weight to the 1.1761 power?
Maybe it’s square root of 1.0845 which is 1.04139! Silly me I did it backwards
Okay now I understand. Going from 30" waist 150lbs to 40" waist makes you 184lbs which seems about right? Very near 6lbs per inch.

TLDR someone needs to make a chart grid of like weight=rows height columns width. I am stinking up this math post.


This is admittedly the weakest part of my post: based on shaky data, has some threshold to switch rates that is never defined, etc. I mostly included it because it’s easy and doesn’t seem to deviate too far within a certain weight category.

Thanks for the extra work! And I will definitely be thinking about dingotush’s proposal

I like how both 1 and 6 are both ‘Don’t’, and took me a minute to realize why I was pinged, haha XD

There is a tool that Khatoblepas has put up on the web for ease of use called The Fat Calculator that helps put into numbers the body shape, though it does require putting in the numbers for both weight, height, and the fat distribution, but it’s pretty good never the less.


Lol. Didn’t realize linking a post would ping the poster! Thank you for the nice words

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There are a lot of factors that can go into how weight gain interacts with clothes. Personal experience was that only 20 pounds were enough to make buttoning old pants nearly impossible, and the top button on shirts would be difficult/choke me.

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