Bra sizing

[Creamcrackersandricecakes]

I'm hoping someone can help me out, as I'm sure I've done this wrong! My 12 year old DD has grown a lot in the last year and needs new bras, as the 28Bs I got her last year won't do up. I measured her using a guide I found online. Her band measurement is 28" and her cup measurement is 33.5". The online calculator put her at size 30F which sounds insane to me - they don't look any bigger than mine and I wear a 32B or C.
I was planning on getting her measured but my local m and s said they don't measure children?

Do boob or bust.

The cup is a measurement of the size of the breast in comparison to the back size. So a 28H is actually a smaller breast size than say a 38D.

If her band measurements is 28", she is a 28 not a 30 for a start.

Please don't go to marks and Spencer.
Boob or bust is the best way to measure.

You might be wearing the wrong size too, lots of women are!

30F is not that big as the cup size is in relation to the band size - so a 30F cup would be smaller than a 34F cup, for example. That's why the usual way of talking about a celebrity being a "D cup" for example means nothing without the band size being mentioned.

If the cup is too small then the band will feel too small as the cups will "steal" fabric from the band. So it's possible she now needs say 28D if her breasts have grown but her rib cage measurement hasn't.

Boob or bust says 28ff. And yes, I think it's safe to say she's only grown in the bust area; her rib cage is the same. We're off to town now, I think we'll see if we can try on a bunch of sizes and go from there. Thank you everyone!!

You won't find that size on the high street, small back size + bigger cup size isn't some thing they stock, a lot of retailers skip sizes too so a bra you pick up won't be true to size.
Brastop online is a good place to look