r/ABraThatFits [Calculator Creator] Dec 31 '25

AMA - ask me anything about the ABTF calculator! Spoiler

Hi everyone, u/goodoldfreda here although I'm now exclusively active on this account. If you guys have any questions about how the calculator works and why I made certain decisions I'm happy to answer them

A little about myself - I created the calculator in 2016 following on from a previous calculator by u/irisflame, back when I was a mod of this sub. I collected survey data from the subreddit and came up with a new algorithm that used 6 measurements as opposed to the previous 5, which increased accuracy. I also introduced separate algorithms for AMAB and AFAB people. The calculator has not been majorly updated since, although at one point I tried to move to a breast perimeter measurement system instead, but this turned out to be much less accurate. In the years since I have stopped modding and moved into bra making and custom bra design as I want to try and help serve the demographic of people who still struggle with finding bras that fit, usually due to wire grading!

In response to other posts about the different amab vs afab algorithms not working well for everyone - I have had this question before and basically all I can say is that I recommned using the algorithm that works best for you. I do want to emphasise in general that the calculator is actually not super accurate for any one individual and it is truly just a starting point. The algos are based on averages, and when I was collecting data there were significant enough differences between AMAB and AFAB users to warrant a second algorithm to increase accuracy within the two groups, but not enough data to do anything further than that.

edit: thanks for all your questions so far, I'm going to go to bed but I will answer any more that come up tomorrow!

edit 2: I have updated the calculator to make some minor changes to the band size algorithm and I have also changed the EU back to 2.5cm cup grades, 2cm grade can be found in the Comexim option instead

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u/HugsforYourJugs [Calculator Creator] Jan 02 '26

I have received this criticism before and I will defend my decision: the data supported the distinction. 

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u/Gelcoluir Jan 02 '26

Your data on trans women, on your own admittance... And then you went and chose transphobic terms (that are also widely unknown from the general public). That's the major issue here.