Wearing a 34A bra when you are actually a 26D is sister sizing

I measured as said to do online in a calculator, and it came out as 28 D, but my breasts look too small to be an A, I'm 13, how do I

Bra Size Calculator India - Find How to Measure Bra Size

People are learning their real bra sizes thanks to a calculator that's gone viral on TikTok

Sister Sizes: The Bra Secret Every Person Should Know – Sister Sizes & Equivalent Bra Size Chart – ThirdLove

Bra Sister Sizes Chart, Sister Cup Sizes Chart

Sister Sizing 101

ThirdLove Bra Size Chart - Find The Perfect Bra For Your Cup Size

My bra size is 34B. Are my breasts smaller than average? - Quora

Is 34A (bra size) really flat? - Quora