Admittedly, I'm not much of an accurate measure but it was around ~16 inches and mine is a 40. I'm not sure if that gets you what you need, I would highly encourage to just ask your SA if they have a similar piece you can try so that you can gauge if the fit might work, or just see if they can bring it in for you to try on. I don't believe your SA can fault you if it just clearly does not fit, is too large, etc. These cardigans and the fit can really be all over the place. In FW2021 alone I took cardigans in size 38, 40 & 42 because of the varying fit. Hope that helps...
I don't have a modeling shot but what you see on the website of these cardigans is very reflective! I think the largest thing to consider is your height. They can come across as a bit long on shorter women depending on the style and fit.