A 28DD is small. VERY small. Its sister sizes are 30C and 32A. A 42DD is massive. The cup is relative to the band size.

Choose the correct bra cup size when changing band size

Understanding Bra Sister Sizes

What is my bra size?

Choose the correct bra cup size when changing band size

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

28C Black Bralette, Bra for Small Breasts, Supportive Bralette, Yoga Bra, Wireless Bra, Petite Bra, Convertible Bralette, Cross Back Bra

What's the next size up after 34A bra? - Quora

Is a 36C bra size big or small? - Quora

What bra size should I try next, I am currently a 42b but the cup wrinkles and is cutting into my sides? - Quora

What do Bra Sizes Mean? – Curvy Kate CA

What is Sister Sizing? – Fleur of England

Which size bra is big, A or B? - Quora

What is the difference between overbust and underbust measurements when it comes to bra sizes? - Quora