Underbust – Band Size Relationship: An Analysis

Howdy y’all! /u/shaytom here!

I know it’s been a while, but hopefully some of you remember my request to fill out a survey regarding underbust measurements and preferred band size. Finally, I have finished analyzing my results and I’m ready to let you all read about my findings.

Fun fact: I couldn’t figure out the best way to post my results, until I thought of doing a blog post. I do not, however, have a blog of my own, and thus, the official blog of /r/ABraThatFits was born!

Now on to the results! Just a heads up, here’s how I’ll be organizing this. I have made graphs/charts for various things regarding the general population, each band size specifically, and comparisons between band sizes. I will first present these visuals one at a time, then just summarize what is implied by each one. At the very end, I will try my best to draw the most general conclusions possible, so for a TL;DR, head to the bottom!

I will discuss limitations at the end, but one thing I wanted to address first is that there were some data points thrown out. These were solely measurement/response errors (ex. BTT was reported as larger than snug). I did not want to assume that they had simply been switched, since it was also possible that one of the entries was a typo, so these kinds of responses were not included in the data set.

First up, General Statistics:

General 1

These two histograms are pretty much just for funsies. Not much insight to gain here, but for those of us that like pretty charts, the band size distribution has a beautiful skew! Also interesting to note that “squish” can get as high as 5″, but the middle 50% of respondents reported a squish between 1 and 2 inches.

General 2

Now we’re actually getting into the relationship between underbust measurements and preferred band size. First, let’s take a look at the top two pie charts.

  1. There seems to be a pretty equal likelihood of wearing a band above, below or equal to the snug measurement. Does this mean that measurement is unnecessary/can’t help us determine the best band size? Not necessarily! Keep reading for more.
  2. A whopping 86% of ABTFers wear a band above their tight! Only 6% wear a band below their tight! Moral of the story: it’s really not a good idea to suggest going below the tight, pretty much ever. There are of course exceptions to the rule, and we will of course be digging deeper for when it is appropriate to go below the BTT.

The second set of pie charts may be a bit more confusing so let me try to make it clear. To make these charts, I calculated how many bands above or below the snug/tight each respondent reported wearing. Specifically, those who wear 2 sizes below measured 4-6″ larger than their band size. Those who wear one size below measured 2-4″ larger; those who wear their exact band size measure +/- <2″ from the band size, etc.

  1. 91% of respondents wear a band size +/- one away from their snug measurement. Don’t stray too far from the snug! ‘Nuff said.
  2. 60% of respondents wear a band one size larger than their BTT measurement. No respondents who wore a band below their BTT went farther than one band down. About a quarter wear 2 sizes larger than the BTT.

General 3

These histograms look specifically at those respondents who reported wearing a band below their BTT (n = 40).

As we can see from the band size distribution, going below the BTT measurement is not solely for “larger” band sizes. The average band size is actually quite close to the center.

As has been shown before, larger cup sizes are more likely to require going below the BTT. The average cup size for those below BTT is between a GG and H (for the curious, cup size was “averaged” by assigning a number to each cup size [A=1, B=2, etc.] and averaging those numbers). There are still some “smaller” cup sizes that still required a band below BTT; however, these may be outliers/anomalies and not necessarily something we should base our general recommendations off of.

TL;DR of General Stats – Going below the BTT is actually quite rare, even for “larger” band sizes. It is, however, more common for larger cup sizes, as we already knew.

26 Bands:

Unfortunately, I did not receive enough responses for 22/24 bands (which is to be expected), but I did have 26 respondents who reported wearing 26 bands. I would have preferred to have at least 30, so take these results with a grain of salt; the sample size is not necessarily large enough to draw general conclusions from.

26 Bands

The average 26 band falls in between their snug and BTT measurements. Note that all respondents who wore bands below their BTT had a difference of less than one inch between their BTT and band size (so none had BTTs lower than 26.75″). While the average cup size for those below BTT was smaller than we might expect, again it is important to keep in mind that n=26 in this case, so outliers can more easily drag the average down.

28 Bands:

28 BandsThe average 28 band measures about 28″ snug, and has a BTT below 28″. N = 131 here, so generalizations are likely to be a bit more accurate than they were for 26 bands. The most interesting fact to me is that only one 28 band wore a band below their BTT; this person’s BTT was 29″ and they wore an F cup. Why is this so different from 26 bands (where 11% [although this was only 3 people] of respondents wore bands below their BTTs)? I have no idea! Anyway, let’s never suggest a 28 band to someone who measures above 28″ BTT.

30 Bands:30 BandsSimilarly to 28 bands, the average 30 band has a snug underbust of about 30″, and you can count the number of women going below the BTT on one hand (in the second largest band size group!). Hmmm, I see a pattern developing!

32 Bands:32 BandsThe pattern continues! A very small percentage of women going below the BTT (and here we see a more typical average cup size of H/HH for those women). The average 32 band has a snug of about 32″ and a BTT of about 30″… same deal as 28/30s! This is the largest band size group, and there are only 3 women going below the BTT.

34 Bands:

34 Bands

Sorry this is getting kind of repetitive, but I did think people would want to look at their own band size for individual reference. Again, we see an extremely small percentage of women going below the BTT, and none more than 1″ lower.

36 Bands:

36 Bands

Oh hey! That’s different! A larger percentage of 36 bands are going below both the snug and BTT underbust. The band size falls pretty squarely in between the average snug and the average BTT. Keep in mind that although there are more women going below the BTT, it’s still less than a quarter of the sample (n=61 for 36 bands). This is still by no means “typical” for 36 bands, but it is certainly getting less unheard of.

38 Bands:

This’ll be the last group by band; no band 40+ had enough respondents to generalize.

38 Bands

So somewhat strangely (and possible due to a smaller sample size; n=24 here), the pattern shift that we saw with the 36 bands hasn’t continued, or at least not to as great of an extent. About half women who wear 38 bands are below their snug measurement, but only 13% are below their BTT.

Comparing The Band Sizes:

I’ve saved the best for last! The following charts really show the gist of what’s happening here.

BB 2

Here we see that the average person falls pretty much right at the snug measurement up to about 34 bands, where it starts to shift to between the snug and BTT. The band size still never falls right at the BTT. Even 36 and 38 bands have an average BTT below their band size.

BB 1

First let’s talk about squish:

There appears to be a slight upward trend as band size increases. A correlation of 0.23 is not very strong, however. We can conclude that there is some relationship between band size and amount of squish (namely, as band size increases, there tends to be more squish) but it doesn’t appear to be that strong of a relationship.

In addition, from the second set of correlations, we see that squish and the difference from snug has a moderate relationship (r = -0.51). Normally what a negative r means is that the more squish, the less of a difference. But since I used negative numbers for difference from snug to mean the band is below the snug, what we’re really seeing here is that squishier women wear a band farther below their snug underbust. Make sense?

However, a correlation of 0.11 is very weak, showing that there isn’t really a relationship at all between how much squish a woman has and where her band falls in relation to her BTT.

Now we’ll discuss the relationship between band size and the differences between underbust measurements.

1. The graph shows a downward trend in difference from snug, but as you can see the correlation between such and band size is not all that strong (r = – 0.22) so while there is some relationship there, it’s not strong enough to say definitively that larger bands require bands farther below their snug.

2. You can see from the graph that the trendline for difference from BTT is nearly horizontal. Since the correlation between band and difference from BTT is extremely weak (r = – 0.09), there is really no relationship between the band size and how far they are from the BTT.

Note that this is the relationship between the difference from underbust measurements. This does not mean that all bands have the same incidence of going below the BTT, but that the amount that they could possibly go below is about the same. For example, as we saw in the general statistics, those who went below the BTT went an average of 1″ below, and no one went more than 2″ (or one full band size) below. You wouldn’t tell a person who measures 30″ BTT to wear a 26 band on any occasion, and you shouldn’t tell a person who measures 40″ BTT to wear a 36 band on any occasion (not that anyone ever has). I hope this part makes sense.

BB 3

Here’s the real meat.

First let’s discuss BTT:

1. You can certainly see a decent downward trend in the % of people who need to go above the BTT as band size increases. The correlation of -0.51 supports this. So less women need to go above the BTT in the larger band sizes, but note that the point of the trendline for 38 bands is still a little above 70%. So basically, just because it’s more likely to occur doesn’t make it the most likely option. Pretty much all women below 34 bands need to go above the BTT, but the number of women above 34 bands who need to go above the BTT is still very high.

2. There is also an upward trend in the % of people who need to go below the BTT, and again the correlation (r = 0.52) supports this. Again, looking at the actual graph we see that the point on the trendline for 38 bands is less than 15%. So while it is certainly more likely that a 38 band will need to go below the BTT than a 28 band, it is still not the most likely option. It is still more likely that the women will need a band above her BTT, since, as mentioned earlier, 70% of 38 bands do.

Now we can discuss snug:

1. There’s a noticeable downward trend in the % of people who need to go above the snug, but the correlation of -0.34 isn’t the strongest. It’s still enough to claim some relationship, so it is less likely that larger bands will go above the snug (only about 20% of 38 bands). Remember that even for smaller bands, less than half go above the snug.

2. The trendline for % of women who go below the snug is practically horizontal again. The correlation is only about -0.1. Note that the trendline hovers around the 50% line. If you’re confused as to why this isn’t just the opposite of the above, remember that there is a 3rd option: being equal to the snug. So if less women need to go above the snug, but the same number of women go below, that means more women are equal to it. Anyway, about half of all women in any band size go below their snug.

General Conclusions:

1. As band size increases, it is more likely that a woman will need to go below her BTT.

2. HOWEVER, even in larger band sizes (36+), less than a quarter of the women go below the BTT. So let’s stop telling people how common it is, and how the band is stretchier and most women in your size can go down a band; this isn’t true. Keep in mind this data represents true to size bands.

3. Keep in mind the data (both from this post and past surveys) that indicate that larger cups (somewhere around G+) need to go closer to their BTT. So if someone measures 36″ BTT and needs a HH cup, sure go ahead and tell her to try a 36 band. If someone measures 36″ BTT and needs a DD cup, she’ll more likely than not prefer a 38 band (remember, my survey asked what band size you prefer).

4. Below 36 bands, the average measurements have a snug equal to their band size. So someone measures 30″ snug and 27″ BTT? Put them in a 30 band. For 36+ bands, the average measurements straddle the band size. So if someone measures 37″ snug and 35″ BTT, don’t size them down to a 34; more likely than not she’ll prefer a 36.

Basically, the trend of suggesting band sizes equal to BTT is really quite inaccurate, particularly in smaller bands. As always, bra fitting is an art, not a science, but that doesn’t mean there aren’t legitimate trends in what measurements correlate to what sizes. Just keep this data in mind the next time you tell someone with a BTT of 32.5″ to start with a 32 band. I think some people might have a fear of suggesting a band equal to the snug, but my data shows that this is actual the typical response (again, below 36 bands). And above 36 bands, even if you do want to suggest something below the snug, that doesn’t mean you should be afraid to go above the BTT; again, this is the typical response.
1. Sample size – Particularly when it comes to certain individual band sizes (26 and 38 bands) the sample size wasn’t huge.
2. Measurement instructions – Though I tried to describe how to measure snug and BTT, there are likely some people who misread, misinterpreted, or didn’t read those instructions at all. Therefore it’s impossible to definitively say that all BTT measurements were really as tight as they should have been.
3. Reported band size – I asked that only women who had been sized correctly and had a bra that fit well in the band reply, but there’s obviously no way to prevent people in an incorrect size from responding. In addition, I asked for people to respond based on true to size brands, but some may have missed that instruction or did not know that a bra they owned didn’t actually run true to size.
Hope you all find this post informative and helpful in guiding your sizing recommendations!

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