I'm a 32F and it fits me well in the chest -- not at all small, not overly roomy. It has a slight A line cut to it, so for me it just feels too voluminous under the bust. I actually think this style might look better on someone less busty because there would be less "tent" effect and it would drape more, IYKWIM.
Laid flat, it's 20" across at the bottom of the armholes. It's 24" across at the hem.