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.

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

Tips for Ordering a Wire Bra

What do Bra Sizes Mean? – Curvy Kate US

What is my bra size?

Understanding Bra Sister Sizes

Everything You Need to Know About Bra Sister Sizes - The Melon Bra

What is my bra size?

Everything You Need to Know About Bra Sister Sizes - The Melon Bra

Petite Friendly Bra, 28C 28D Bras