Bra Science — Why The Two Finger and One Inch Rules Don't Work

Note: This post is operating under the premise that only the band size is being tested when checking a bra fits correctly. As too small cups can make a band feel too tight due to breast tissue not being fully contained/general constriction of the bust, I always advise checking band fit with the bra fastened backwards and/or upside down, as this removes the cup fit from the equation.

A lot of bra resources on the internet (including Bustyresources, Bratabase, and so many company fitting guides) have ways of determining if a band fits you based on how far it stretches out. Here are the two most common variations of this rule:

1. You should be able to stretch the band out 1" away from your ribcage (when fastened on the loosest hooks)
2. You should be able to fit two fingers comfortably under the band (when fastened on the loosest hooks)

While I don't deny that these rules can help people understand that a band is supposed to be snug, and can work in the extremes, I don't believe these rules hold any water in the vast majority of cases.

Before I can test the premise, we first have to define what means a band is the right size:

A band that fits is snug enough to support most of the weight of the bust and doesn't slip around, but loose enough that it causes no discomfort, with comfort being the most important factor.

There's no perfect way to define such a subjective thing (and I stress that it is very subjective), but I feel like that's pretty good. It's also important to note that some people are especially sensitive to snug materials, so size up in the band, sacrificing support and security for comfort. Is this a poor/incorrect fit? Some bra fitting enthusiasts believe so. But I don't think it is, it's just a different standard - and not really a different standard at all if you put comfort above all else. 

Immediately you can see a couple of flaws with these rules - often, people with larger busts opt for a snugger band, and people with smaller busts a looser one. People have different amounts of strength - how much strain should be put on a band to stretch it  by x amount? How can you apply a one-size-fits-all  rule to arguably the most individual aspect of bra fitting? Let's take those criticisms and put them to one side for now, because I want to see if these rules work in even a majority of cases. I've come up with a small experiment to see if they do!

The Test:

Now, because a band should be, first and foremost, comfortable, it should be able to handle wrapping around my ribcage at a comfortable size. For me, a snug but comfortable ribcage measurement on a neutral inhale is 25.5" (let's call this measurement A), but a bra should be able to have a bit more stretch in it to accommodate my breathing - my snug ribcage measurement on an inhale is 26" (let's call this measurement B). Thus it logically follows that ideally it shouldn't stretch to much more or much less than that second measurement, and if it's less than the first it's going to be uncomfortable all the time. 

So it follows that, provided these rules are correct, I can do the following:

1. I can wrap a measuring tape as tightly as possible around my ribcage to emulate the smallest length a band could stretch to to fit around my ribcage (a very snug band!).
2. I can apply these tests, and if I extend the tape so that they pass (because the tape is inelastic)
3. Then the measurements on the tape when applying these tests should at least be bigger than A, and should be around B. 

I haven't included a way to test if a band is too large, because tapes slip.  But let's just go with testing if a band is too small for now. 

My Results:

Note: I wore a poorly fitting 28G Freya Daydreamer Balcony-Plunge on the loosest hooks when taking these measurements, as I wanted to ensure as well as I could that my measurements weren't being affected by a bra. If you test this on yourself, you should probably freeboob it.

Measurement A: 25.5". My neutral, comfortable but snug underbust.

Measurement B: 26.75". My comfortably snug inhaling underbust. Look at those lungs go!

Let's get this tape as tight as possible!

Measurement C: 23.5". That's about as small as I could manage for my tight-as-possible underbust.

You can't really see my fingers here but trust me, they're under the tape

Measurement D: 23.8". Keeping the tape as tight as possible, I put two fingers underneath it. The tape now "passes" the two finger test.

Angle looks weird but I've done this multiple times and this is pretty much the result I get every time

Measurement E: 24.75". I kept the tape as tight as possible but pulled it out an inch. Hard to do, but I'm pretty sure this is the smallest measurement that will "pass" the 1" test on me.

So if a band size passes the two finger test, I won't necessarily be neutrally comfortable in it - it'd have to stretch to 1.7" more than that to be neutrally comfortable. And forget about breathing!
If a band size passes the 1" test, I wouldn't necessarily be neutrally comfortable in it - it'd need to stretch to 0.75" more than that to be neutrally comfortable in, and 2" more if breathing is something I'd like to participate in.

Now, at the moment, you're probably thinking: "But hey, Hugs for Your Jugs, you're just one person. Everyone knows that for any kind of scientific experiment on humans to be respected, you have to have a large sample size."

True, but these rules are never quoted with any exceptions. Since they don't work for me, they should at least be revised to say they don't work every time.

Also, I am a person who doesn't have much fat on their ribcage. Thus, my ribcage is (probably) less compressible than average. Since this means that my emulated "very snug band" is larger than most other people's in proportion to measurement A, if this doesn't work on me, then it probably doesn't work for a majority of the population. However that is just speculation, there could be other factors involved that I'm not considering.

Also also, here are some friends and other bra fitting enthusiasts with different body types to me and their results...

Other Results:

noys:

A: 32"

B: 34.5" (She told me she went all out on this one!)

C: 30.6"

D: 31"

E: 31.5"

As you can see, neither the 2 finger test nor the 1" test measured the same as her comfortably snug neutral measurement, and forget about her inhaled measurement. The 1" test was close to her comfortably snug but close doesn't cut it!

ladyverene:

A: 36.5"

B: 38"

C: 34.5"

D: 35.5"

E: 36"

Again, neither the 2 finger test nor the 1" test measure the same as her comfortably snug neutral measurement, and they're 2" to 2.5" off her inhaling underbust measurement. A band that passes both of these tests could still be pretty uncomfortable!

fattireflattire:

A: 30"

B: 31"

C: 28.2"

D: 29"

E: 29.8"

The 1" test certainly comes close to her underbust measurement, so perhaps a bra that passes the 1" test for her would be all right for short spurts of wear, but it would probably be difficult to breathe comfortably in. The 2 finger test doesn't come close to her snug, neutral underbust, let alone her breathing underbust.

anon:

A: 32.75"
B: 34.5" (she says she took a deep breath for this one)
C: 31" 
D: 32"
E: 32.25"

Again, neither tests reach the neutral underbust measurement. The 1" test is only half an inch off, but that would still probably be uncomfortable to sit in and, you know, breathe in. 

Conclusion:

I understand there are a few limitations to this test - for instance, you can probably cinch a measuring tape tighter than a bra band, but frankly it's the best thing I can come up with, and I really doubt it would affect the results enough to show that you can breathe in the bands comfortably if they pass the tests.

So it seems that these tests don't have much (any?) basis in reality. A band that you can pull out by one inch or can fit two fingers under probably won't stretch to an amount that you can be neutrally comfortable in, or actually breathe. And call me old fashioned but I think breathing is pretty important. It's probably better listening to how a person feels in the bra than relying on inaccurate tests like this!

Do these tests work for you? Is there a way I can improve these tests? I'd love to hear your feedback!