The different sizing systems bra brands use to classify their cup sizes is a common nuisance. Figuring out if your G cup is actually a G, or an H or an I cup in another brand does not make things easy.
It is easier if you are a D cup of below. Bra brands, regardless of sizing systems (EU, FR, UK, US, etc), size their bras consistent from A to D.
This chart is no sure thing! Remember, when switching brands, buying the same size does not guarantee a proper fit.
Still, many of us love to spend time online browsing bras, guessing, perusing. This chart is to help you in case you want to make some broad assumptions about fit and size.