A 28DD is small. VERY small. Its sister sizes are 30C and 32A. A

Know Your Bra Sister Size – Bratag

Bra Sister Size Calculator - Cuddl

Cosabella Never Say Never Curvy Sweetie Bralette

What is my bra size?

What Are Bra Sister Sizes And Why Do They Matter? - SHEFIT

What bra size is equivalent to a 28C? - Quora

30C White Bralette, White Sports Bra, Workout Bra, Yoga Bra, Comfortable Sleep Bra, Supportive Bralette, Bra for Small Breasts, Convertible - Denmark

Bra size - Wikipedia

Bra size - Wikipedia

How to Measure Bra Size, Bra & Knicker Types

How to Measure Bra Size, Bra & Knicker Types

True & Co. True Everybody Women's Adjustable Strap Scoop Neck Bra

Sister Sizes, Bra Fit Guide & Size Charts