Size down at least once. You can size down one more if not super busty. Ash is a 16/17 and 40h busy wearing the large  

Details

SQUARE NECK WITH ADJUSTABLE STRAP GATHERED DETAIL WITH SMOCKED WAIST MAXI DRESS

Brand:  Heimish

Color: Black

Sizing

S (2-6) | M (8-10) | L (12-14) | 1X (16-18) | 2X (20-22) | 3X (22-24)

Ashley (Size 16 regular and 40H bust) wears size Large 

Fabric Fit & Feel

100% Poly 

Relaxed fit with room in the tummy (Taco friendly :-) 

Measurements (approximate and taken while laying flat)

Length from shoulder to bottom seam: Medium 46 Inches | 2X 48 Inches

Bust width: Medium 30 Inches | 2X 36 Inches