Light bathing suit, nightgown weight, polyester spandex wrap dress with halter neck tie.
I measured it folded with enough fabric to cover and stay wrapped and that’s about an 18 flat. Im a small 14 and this did not cover me but just. I’d say an 8-10 is about right.

Here are the exact dimensions of the piece of fabric. All hemmed.
50 wide x 46 long in back.
Wrap top straps 24 inches to tie

This item is sold from an excellent, highly rated vintage boutique in Portland, Or.