Depending on the brand and style I can be DD, E, F or G. I came up a G on this one.
I am a certified bra fitter specialist in real life, and while the methods are all the same, you also have brands and styles you think of when sizing. On one of the days I do this as a freelancer (meaning I am a fitter in a store and paid, but not an employee) I know the brands that they sell. I actually wear one of the brands they sell. In that brand and style I am a 38DD. I switch to a different brand and style (plunging in this case and a higher end designer) I am a 36 G. Another brand and style (t-shirt and at this point all my bras cost between 50-100 USD) I am a 40 E. I also usually have to do some alteration to the bra itself to fit perfectly (usually I add a bra sling or at a minimum take in the center gore).
There is no one size fits all to bra fitting. Angled cups can push them forward, and cost of what you are willing to spend can play into what you need/get.