This is less straightforward than it might seem. In the USA plus size departments start their size range at 14/16, 14W, or 1X. Regular or “Missy” departments often go up to a size 16, sometimes even a size 18 (or XXL). So if you wear a US size 14, 16 or 18, chances are high that you shop in both Missy and Plus in order to find a garment that fits.
I see this first hand with my clients who wear sizes 14 to 18. They shop all over the show. Sometimes they can wear the largest size in Missy, or the smallest size in Plus, which is great because it gives them a larger assortment of merchandise to choose from. But sometimes the opposite holds true when they are “between” departments. Size 14 and 16 gals often find that the largest size in Missy is too small but the smallest size in Plus is too large. Intuitively, you’d expect that the smallest size in Plus would be cut a size up from the largest size in Missy. But it’s actually cut wider and larger everywhere, and is not just an even size up. So things don’t end up fitting at all.
It’s very frustrating when you are in-between department sizes. The solution is to keep on searching and fitting all sorts of clothing brands until you find Missy size garments that are cut larger and Plus size garments that are cut smaller. I also sometimes suggest having slightly too large Plus size items altered to fit. It’s a time-consuming process, but we end up finding great items eventually.
If I were in a position to design and manufacture a clothing line, I would make a range from sizes 14 to 18 across petite, regular and tall lengths my specialty. Seeing as the average American woman wears a size 14 dress, it would make sense for someone in retail to tackle this HUGE gap in the market right away.