I normally wear a 16W, but as this is a sheath dress, I sized up )18 W) as I am large chested (40 DDD) and have large thighs. I had to take it up about a 2 inches in the side. I think the dress is true to size.
I wore this with a crocheted long shrug to my husband's promotion ceremony, in Savannah, outdoors. The heat index was 110 that day. The dress was cool and easy to move in. I got several compliments on it!