Beautiful Alex Colman California Vintage 1960s Dress. Mod/Boho Brown and Black Floral Pattern on White. Sleeveless, knee-length style. Lightweight material. Zips in the back. In excellent condition from a smoke-free, pet-free home.
This dress does not list a size, but I'd say it's probably L or XL.  Here are the approximate measurements:

Bust: 39 inches
Waist: 36 inches
Length (from top of sleeve to bottom hem): 37 inches