Fit
Size guide
One rule covers most of it: buy the insert that matches the cup you wear now, not the cup you want to end up in.
Why the insert matches your current size
The insert is what creates the change. If you buy a size up expecting more lift, you get a piece that does not sit flat in the cup and shows a ridge at the top. The size on the box is the cup it fits into, not the cup it produces.
How the band works
It does not, for the insert. Band size changes how a bra fits your ribcage; the insert only cares about the cup. A 30C and a 38C take the same insert. We ask for the band in the finder only so we can print the size back to you in the format you recognise.
Still not sure
Send us the bra size you wear most often and what you are trying to wear it under. That is usually enough for us to answer properly, and it is faster than guessing.