Women's Jonathan Martin black and white polka dot dress size?

The dress has an empire waist with embroidered flowers at the waist. There's a side hidden zipper and back tie. The flutter sleeves are open at the shoulder. The tulip bottom adds a pretty touch. Excellent condition from a pet free and smoke free home. Unfortunately the size tag has been cut out but I'll provide measurements. Pit to pit is 20, waist is 18, pit to bottom is 36 and overall length from shoulder to bottom is 46.5.