The mystery of underwire sizes

[Beeches]

Does anyone know whether underwires scale up and down in size along with the cup sizes? I know that small band bars with small cups have correspondingly small radius underwires, so assume that big bands must also mean big wires.

I ask because I am still in search of a better bra (like everyone else that wears them, I suspect). I was thinking about sister-sizing to try to containing a little more of my side boob tissue. I figured that if I went up a band size and dropped a cup size, the underwire, and thus cup shape would suit my breast shape better. That's my theory, but I'm new to all this and may have got my bra theory completely wrong.

Like many here I have wideset, shallow boobs and thought that the above plan might result in a better fit. Has anyone tried this?

[OHboobs]

I am no expert on bras, and certainly not underwire bras.  But seems to me, the underwire size would be more dependent on band size than cup size.

[curiousk]

I think the best thing to do is to get professionally fitted.   They can show you all of the different kinds of bras that will do the things you want your bra to do for you.

[Beeches]

Thanks, OHboobs. That’s kind of how I was thinking - it seems logical that the underwire would get bigger along with the band, so if that is the case, my plan may work...

Thanks also curiousk. Yeah, I absolutely know I should get fitted, and one day I will. Between living in a VERY rural location where everyone knows your business, and ongoing concerns about the Coronavirus, I’m too concerned to go and do it right now. I’m not even sure if I could get a fitting right now. But you are right - it is the only way to know if what you’re trying to achieve is right.

[Bosh808]

I'm not sure my self, I've always thought the the underwire size goes with cup size and not band size. 
For awhile I was wearing 38c and it fit ok depending on the bra but after getting a fitting, it turned out that 42b works better. 
Since 42 band size is rare, I usually get 38b and use extenders. 

[Johndoe1]

I believe it's correct that wire size goes with cup size but it can also depend on style as well. If you want the wire to extend further back under the arm pit, then you would need to increase cup size but you will also need to decrease band size. Obviously there's a limit on how much you can sister size, that's when style and cut of the bra comes into play. Different manufacturers will also use different shape wires from style to style depending on body shape. Wires can be complicated at times.