Answer (1 of 4): Well, I don't know how this sister sizes ( in relation like sister companies etc,,) ever became as you describe..There is nothing remotely close to each of those sizes. Mathematically and according to any standardized charts ..Remember one very important rule in life .Mathematics
ThirdLove Bra Size Chart - Find The Perfect Bra For Your Cup Size
What are sister bra sizes? - Quora
Explained: What is Bra Sister Size with Sister Size Charts
How to figure the right size of bra? 34c is too tight and the cup is large. Google measurements shows 36c is suitable. Is it - Quora
How come I can fit both on a 36C and a 36D bra size? - Quora
What Are Bra Sister Sizes? – Harlow & Fox
Which implant size would be best, 32C or 32D? - Quora
10 Bra Tips
What is the difference between 34D and 32D? I have been wearing 34D only to be told on a 32D. - Quora
Bra Sister Sizes - Unlocking The #1 Secret to Your Perfect Fitting Bra - Bra Space
What is the difference between 34D and 32D? I have been wearing 34D only to be told on a 32D. - Quora
What Are Bra Sister Sizes? – Harlow & Fox